diff --git a/.idea/php-test-framework.xml b/.idea/php-test-framework.xml
new file mode 100644
index 0000000..e47438f
--- /dev/null
+++ b/.idea/php-test-framework.xml
@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="PhpTestFrameworkVersionCache">
+    <tools_cache>
+      <tool tool_name="PHPUnit">
+        <cache>
+          <versions>
+            <info id="Local" version="8.1.6" />
+          </versions>
+        </cache>
+      </tool>
+    </tools_cache>
+  </component>
+</project>
\ No newline at end of file
diff --git a/.idea/php.xml b/.idea/php.xml
index f6159c8..f19075c 100644
--- a/.idea/php.xml
+++ b/.idea/php.xml
@@ -1,4 +1,9 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
   <component name="PhpProjectSharedConfiguration" php_language_level="7.3" />
+  <component name="PhpUnit">
+    <phpunit_settings>
+      <PhpUnitSettings load_method="PHPUNIT_PHAR" bootstrap_file_path="$PROJECT_DIR$/src/autoload.php" configuration_file_path="$PROJECT_DIR$/phpunit.xml" custom_loader_path="$PROJECT_DIR$/tools/phpunit" phpunit_phar_path="$PROJECT_DIR$/tools/phpunit" use_bootstrap_file="true" use_configuration_file="true" />
+    </phpunit_settings>
+  </component>
 </project>
\ No newline at end of file
diff --git a/src/Bread.php b/src/Bread.php
new file mode 100644
index 0000000..674db1e
--- /dev/null
+++ b/src/Bread.php
@@ -0,0 +1,8 @@
+<?php declare(strict_types=1);
+
+namespace ClansOfCaledonia;
+
+final class Bread extends Good
+{
+
+}
\ No newline at end of file
diff --git a/src/Cheese.php b/src/Cheese.php
new file mode 100644
index 0000000..5126089
--- /dev/null
+++ b/src/Cheese.php
@@ -0,0 +1,8 @@
+<?php declare(strict_types=1);
+
+namespace ClansOfCaledonia;
+
+final class Cheese extends Good
+{
+
+}
\ No newline at end of file
diff --git a/src/Good.php b/src/Good.php
index 2e540c6..9a14569 100644
--- a/src/Good.php
+++ b/src/Good.php
@@ -3,13 +3,4 @@
 
 abstract class Good
 {
-    public static function milk(): self
-    {
-        return new Milk;
-    }
-
-    public function isMilk(): bool
-    {
-        return false;
-    }
 }
diff --git a/src/Grain.php b/src/Grain.php
new file mode 100644
index 0000000..5586838
--- /dev/null
+++ b/src/Grain.php
@@ -0,0 +1,8 @@
+<?php declare(strict_types=1);
+
+namespace ClansOfCaledonia;
+
+final class Grain extends Good
+{
+
+}
\ No newline at end of file
diff --git a/src/Market.php b/src/Market.php
index cfe5ae3..7673528 100644
--- a/src/Market.php
+++ b/src/Market.php
@@ -3,16 +3,38 @@
 
 final class Market
 {
-    public function priceFor(Good $milk): Pound
+    /** @var PriceListCollection */
+    private $priceListCollection;
+
+    public function __construct(PriceListCollection $priceListCollection)
+    {
+        $this->priceListCollection = $priceListCollection;
+    }
+
+    public function priceFor(Good $good): Pound
     {
-        return new Pound(5);
+        return $this->priceListCollection->currentFor($good);
     }
 
     public function sellTo(Offer $offer): Pound
     {
-        return new Pound(
-            $offer->amount()->amount() *
-            $this->priceFor($offer->good())->amount()
-        );
+        $cost = $this
+            ->priceFor($offer->good())
+            ->mult($offer->amount()->amount());
+
+        $this->priceListCollection->moveFor($offer->good(), -$offer->amount()->amount());
+
+        return $cost;
+    }
+
+    public function buyFrom(Offer $offer): Pound
+    {
+        $cost = $this
+            ->priceFor($offer->good())
+            ->mult($offer->amount()->amount());
+
+        $this->priceListCollection->moveFor($offer->good(), $offer->amount()->amount());
+
+        return $cost;
     }
 }
diff --git a/src/Milk.php b/src/Milk.php
index 8689abe..33e7410 100644
--- a/src/Milk.php
+++ b/src/Milk.php
@@ -3,8 +3,4 @@
 
 final class Milk extends Good
 {
-    public function isMilk(): bool
-    {
-        return true;
-    }
 }
diff --git a/src/Pound.php b/src/Pound.php
index 1be124e..c1fe52e 100644
--- a/src/Pound.php
+++ b/src/Pound.php
@@ -17,4 +17,9 @@ public function amount(): int
     {
         return $this->amount;
     }
+
+    public function mult(int $multiplier): Pound
+    {
+        return new Pound($this->amount * $multiplier);
+    }
 }
diff --git a/src/PriceList.php b/src/PriceList.php
index 8a6a231..f98e330 100644
--- a/src/PriceList.php
+++ b/src/PriceList.php
@@ -30,4 +30,25 @@ public function current(): Pound
     {
         return $this->prices[$this->position];
     }
+
+    public function move(int $positions): Pound
+    {
+        $nextPosition = $this->position + $positions;
+
+        if ($nextPosition >= count($this->prices)) {
+            $this->position = count($this->prices) - 1;
+
+            return $this->current();
+        }
+
+        if ($nextPosition < 0) {
+            $this->position = 0;
+
+            return $this->current();
+        }
+
+        $this->position = $nextPosition;
+
+        return $this->current();
+    }
 }
diff --git a/src/PriceListBuilder.php b/src/PriceListBuilder.php
index bc0da06..1bf3efe 100644
--- a/src/PriceListBuilder.php
+++ b/src/PriceListBuilder.php
@@ -15,7 +15,87 @@ public function milkPrices(): PriceList
             new Pound(7),
             new Pound(7),
             new Pound(8),
-            new Pound(8)
+            new Pound(8),
         );
     }
+
+    public function woolPrices(): PriceList
+    {
+        return PriceList::fromList(
+            new Pound(3),
+            new Pound(3),
+            new Pound(4),
+            new Pound(4),
+            new Pound(5),
+            new Pound(5),
+            new Pound(6),
+            new Pound(6),
+            new Pound(7),
+            new Pound(8),
+        );
+    }
+
+    public function grainPrices(): PriceList
+    {
+        return PriceList::fromList(
+            new Pound(3),
+            new Pound(3),
+            new Pound(4),
+            new Pound(5),
+            new Pound(6),
+            new Pound(6),
+            new Pound(7),
+            new Pound(7),
+            new Pound(8),
+            new Pound(8),
+        );
+    }
+
+    public function breadPrices(): PriceList
+    {
+        return PriceList::fromList(
+            new Pound(7),
+            new Pound(8),
+            new Pound(9),
+            new Pound(10),
+            new Pound(11),
+            new Pound(11),
+            new Pound(12),
+            new Pound(13),
+            new Pound(14),
+            new Pound(15),
+            );
+    }
+
+    public function cheesePrices(): PriceList
+    {
+        return PriceList::fromList(
+            new Pound(7),
+            new Pound(8),
+            new Pound(9),
+            new Pound(10),
+            new Pound(11),
+            new Pound(12),
+            new Pound(13),
+            new Pound(14),
+            new Pound(14),
+            new Pound(15),
+            );
+    }
+
+    public function whiskyPrices(): PriceList
+    {
+        return PriceList::fromList(
+            new Pound(7),
+            new Pound(8),
+            new Pound(9),
+            new Pound(10),
+            new Pound(11),
+            new Pound(12),
+            new Pound(13),
+            new Pound(14),
+            new Pound(15),
+            new Pound(16),
+            );
+    }
 }
diff --git a/src/PriceListCollection.php b/src/PriceListCollection.php
new file mode 100644
index 0000000..c4e0707
--- /dev/null
+++ b/src/PriceListCollection.php
@@ -0,0 +1,44 @@
+<?php declare(strict_types=1);
+
+namespace ClansOfCaledonia;
+
+use function get_class;
+use InvalidArgumentException;
+use function sprintf;
+
+final class PriceListCollection
+{
+    /** @var PriceList[] */
+    private $priceLists;
+
+    public function __construct()
+    {
+        $this->priceLists = [];
+    }
+
+    public function registerPriceListForGood(Good $good, PriceList $priceList): void
+    {
+        $this->priceLists[get_class($good)] = $priceList;
+    }
+
+    public function currentFor(Good $good): Pound
+    {
+        $this->ensureGoodHasPriceList($good);
+
+        return $this->priceLists[get_class($good)]->current();
+    }
+
+    public function moveFor(Good $good, int $positions): Pound
+    {
+        $this->ensureGoodHasPriceList($good);
+
+        return $this->priceLists[get_class($good)]->move($positions);
+    }
+
+    private function ensureGoodHasPriceList(Good $good): void
+    {
+        if (!isset($this->priceLists[get_class($good)])) {
+            throw new InvalidArgumentException(sprintf("Good: %s is unknown", get_class($good)));
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/Whisky.php b/src/Whisky.php
new file mode 100644
index 0000000..fd67901
--- /dev/null
+++ b/src/Whisky.php
@@ -0,0 +1,8 @@
+<?php declare(strict_types=1);
+
+namespace ClansOfCaledonia;
+
+final class Whisky extends Good
+{
+
+}
\ No newline at end of file
diff --git a/src/Wool.php b/src/Wool.php
new file mode 100644
index 0000000..847a5a3
--- /dev/null
+++ b/src/Wool.php
@@ -0,0 +1,8 @@
+<?php declare(strict_types=1);
+
+namespace  ClansOfCaledonia;
+
+final class Wool extends Good
+{
+
+}
\ No newline at end of file
diff --git a/src/autoload.php b/src/autoload.php
index 1078cb5..fa00726 100644
--- a/src/autoload.php
+++ b/src/autoload.php
@@ -16,7 +16,9 @@ function($class) {
                 'clansofcaledonia\\pound' => '/Pound.php',
                 'clansofcaledonia\\pricelist' => '/PriceList.php',
                 'clansofcaledonia\\pricelistbuilder' => '/PriceListBuilder.php',
-                'clansofcaledonia\\unit' => '/Unit.php'
+                'clansofcaledonia\\unit' => '/Unit.php',
+                'clansofcaledonia\\pricelistcollection' => '/PriceListCollection.php',
+                'clansofcaledonia\\wool' => '/Wool.php'
             );
         }
         $cn = strtolower($class);
diff --git a/tests/GoodTest.php b/tests/GoodTest.php
deleted file mode 100644
index f44ff47..0000000
--- a/tests/GoodTest.php
+++ /dev/null
@@ -1,18 +0,0 @@
-<?php declare(strict_types=1);
-namespace ClansOfCaledonia;
-
-use PHPUnit\Framework\TestCase;
-
-/**
- * @covers \ClansOfCaledonia\Good
- * @covers \ClansOfCaledonia\Milk
- */
-final class GoodTest extends TestCase
-{
-    public function testCanBeMilk(): void
-    {
-        $milk = Good::milk();
-
-        $this->assertTrue($milk->isMilk());
-    }
-}
diff --git a/tests/MarketTest.php b/tests/MarketTest.php
index d01128e..22605b3 100644
--- a/tests/MarketTest.php
+++ b/tests/MarketTest.php
@@ -10,24 +10,41 @@
  * @uses \ClansOfCaledonia\Good
  * @uses \ClansOfCaledonia\Offer
  * @uses \ClansOfCaledonia\Unit
+ * @uses \ClansOfCaledonia\PriceList
+ * @uses \ClansOfCaledonia\PriceListCollection
+ * @uses \ClansOfCaledonia\PriceListBuilder
  */
 final class MarketTest extends TestCase
 {
     public function testMilkCosts5PoundsInitially(): void
     {
-        $market = new Market;
+        $milk = new Milk();
+        $priceListBuilder = new PriceListBuilder();
+        $milkPrices = $priceListBuilder->milkPrices();
 
-        $this->assertEquals(new Pound(5), $market->priceFor(Good::milk()));
+        $priceListCollection = new PriceListCollection();
+        $priceListCollection->registerPriceListForGood($milk, $milkPrices);
+
+        $market = new Market($priceListCollection);
+
+        $this->assertEquals(new Pound(5), $market->priceFor($milk));
     }
 
     public function testMilkCanBeSoldToTheMarket(): Market
     {
-        $market = new Market;
+        $milk = new Milk();
+        $priceListBuilder = new PriceListBuilder();
+        $milkPrices = $priceListBuilder->milkPrices();
+
+        $priceListCollection = new PriceListCollection();
+        $priceListCollection->registerPriceListForGood($milk, $milkPrices);
+
+        $market = new Market($priceListCollection);
 
         $payment = $market->sellTo(
             new Offer(
                 new Unit(2),
-                Good::milk()
+                $milk
             )
         );
 
@@ -36,11 +53,45 @@ public function testMilkCanBeSoldToTheMarket(): Market
         return $market;
     }
 
-    /**
-     * @depends testMilkCanBeSoldToTheMarket
-     */
-    public function testSellingMilkToTheMarketReducesMilkPrice(Market $market): void
+    public function testSellingMilkToTheMarketReducesMilkPrice(): void
     {
-        $this->assertEquals(new Pound(4), $market->priceFor(Good::milk()));
+        $milk = new Milk();
+        $priceListBuilder = new PriceListBuilder();
+        $milkPrices = $priceListBuilder->milkPrices();
+
+        $priceListCollection = new PriceListCollection();
+        $priceListCollection->registerPriceListForGood($milk, $milkPrices);
+
+        $market = new Market($priceListCollection);
+
+        $offer = new Offer(
+            new Unit(3),
+            $milk
+        );
+
+        $market->sellTo($offer);
+
+        $this->assertEquals(new Pound(3), $milkPrices->current());
+    }
+
+    public function testBuyingMilkFromTheMarketIncresesMilkPrice(): void
+    {
+        $milk = new Milk();
+        $priceListBuilder = new PriceListBuilder();
+        $milkPrices = $priceListBuilder->milkPrices();
+
+        $priceListCollection = new PriceListCollection();
+        $priceListCollection->registerPriceListForGood($milk, $milkPrices);
+
+        $market = new Market($priceListCollection);
+
+        $offer = new Offer(
+            new Unit(3),
+            $milk
+        );
+
+        $market->buyFrom($offer);
+
+        $this->assertEquals(new Pound(7), $milkPrices->current());
     }
 }
diff --git a/tests/OfferTest.php b/tests/OfferTest.php
index 9c0e029..0810160 100644
--- a/tests/OfferTest.php
+++ b/tests/OfferTest.php
@@ -13,8 +13,15 @@ final class OfferTest extends TestCase
 {
     public function testHasAmount(): void
     {
-        $offer = new Offer(new Unit(1), Good::milk());
+        $offer = new Offer(new Unit(1), new Milk());
 
         $this->assertEquals(new Unit(1), $offer->amount());
     }
+
+    public function testHasGood(): void
+    {
+        $offer = new Offer(new Unit(1), new Milk());
+
+        $this->assertEquals(new Milk(), $offer->good());
+    }
 }
diff --git a/tests/PoundTest.php b/tests/PoundTest.php
index 3d3ec6d..37b0425 100644
--- a/tests/PoundTest.php
+++ b/tests/PoundTest.php
@@ -16,4 +16,14 @@ public function testHasAmount(): void
 
         $this->assertSame($amount, $p->amount());
     }
+
+    public function testMultiply(): void
+    {
+        $amount = 100;
+
+        $p = new Pound($amount);
+        $newPound = $p->mult(5);
+
+        $this->assertSame(500, $newPound->amount());
+    }
 }
diff --git a/tests/PriceListBuilderTest.php b/tests/PriceListBuilderTest.php
index 5df7e04..f69b689 100644
--- a/tests/PriceListBuilderTest.php
+++ b/tests/PriceListBuilderTest.php
@@ -19,4 +19,49 @@ public function testCanBuildMilkPriceList(): void
 
         $this->assertEquals(new Pound(5), $milkPrices->current());
     }
+
+    public function testCanBuildBreadPriceList(): void
+    {
+        $builder = new PriceListBuilder;
+
+        $breadPrices = $builder->breadPrices();
+
+        $this->assertEquals(new Pound(10), $breadPrices->current());
+    }
+
+    public function testCanBuildWoolPriceList(): void
+    {
+        $builder = new PriceListBuilder;
+
+        $woolPrices = $builder->woolPrices();
+
+        $this->assertEquals(new Pound(4), $woolPrices->current());
+    }
+
+    public function testCanBuildCheesePriceList(): void
+    {
+        $builder = new PriceListBuilder;
+
+        $cheesePrices = $builder->cheesePrices();
+
+        $this->assertEquals(new Pound(10), $cheesePrices->current());
+    }
+
+    public function testCanBuildWhiskyPriceList(): void
+    {
+        $builder = new PriceListBuilder;
+
+        $whiskyPrices = $builder->whiskyPrices();
+
+        $this->assertEquals(new Pound(10), $whiskyPrices->current());
+    }
+
+    public function testCanBuildGrainPriceList(): void
+    {
+        $builder = new PriceListBuilder;
+
+        $grainPrices = $builder->grainPrices();
+
+        $this->assertEquals(new Pound(5), $grainPrices->current());
+    }
 }
diff --git a/tests/PriceListCollectionTest.php b/tests/PriceListCollectionTest.php
new file mode 100644
index 0000000..4de6a0f
--- /dev/null
+++ b/tests/PriceListCollectionTest.php
@@ -0,0 +1,55 @@
+<?php declare(strict_types=1);
+
+namespace ClansOfCaledonia;
+
+use InvalidArgumentException;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * @covers \ClansOfCaledonia\PriceListCollection
+ *
+ * @uses \ClansOfCaledonia\PriceList
+ * @uses \ClansOfCaledonia\PriceListBuilder
+ * @uses \ClansOfCaledonia\Milk
+ * @uses \ClansOfCaledonia\Wool
+ * @uses \ClansOfCaledonia\Pound
+ */
+final class PriceListCollectionTest extends TestCase
+{
+    public function testRegisterPriceListForGood(): void
+    {
+        $milk = new Milk();
+        $priceListBuilder = new PriceListBuilder;
+        $milkPriceList = $priceListBuilder->milkPrices();
+        $priceListCollection = new PriceListCollection();
+        $priceListCollection->registerPriceListForGood(new Milk(), $milkPriceList);
+
+        $this->assertEquals($milkPriceList->current(), $priceListCollection->currentFor($milk));
+    }
+
+    public function testMoveForGood(): void
+    {
+        $position = 3;
+        $milk = new Milk();
+        $priceListBuilder = new PriceListBuilder;
+        $milkPriceList = $priceListBuilder->milkPrices();
+        $priceListCollection = new PriceListCollection();
+        $priceListCollection->registerPriceListForGood(new Milk(), $milkPriceList);
+        $priceListCollection->moveFor($milk, $position);
+
+        $this->assertEquals($milkPriceList->current(), $priceListCollection->currentFor($milk));
+    }
+
+    public function testUnregisteredGood(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+
+        $position = 3;
+        $wool = new Wool();
+        $priceListBuilder = new PriceListBuilder;
+        $milkPriceList = $priceListBuilder->milkPrices();
+        $priceListCollection = new PriceListCollection();
+        $priceListCollection->registerPriceListForGood(new Milk(), $milkPriceList);
+        $priceListCollection->moveFor($wool, $position);
+    }
+}
\ No newline at end of file
diff --git a/tests/PriceListTest.php b/tests/PriceListTest.php
index aba7abb..93f5141 100644
--- a/tests/PriceListTest.php
+++ b/tests/PriceListTest.php
@@ -27,4 +27,40 @@ public function testHasInitialPrice(): void
 
         $this->assertEquals(new Pound(4), $prices->current());
     }
+
+    public function dataProviderForMovePostionUp(): array
+    {
+        return [
+            [6, 2],
+            [4, 0],
+            [10, 6],
+            [10, 100],
+            [1, -100],
+            [2, -2],
+            [1, -4],
+        ];
+    }
+
+    /**
+     * @param int $expectedPound
+     * @param int $positionsToMove
+     * @dataProvider dataProviderForMovePostionUp
+     */
+    public function testMovePostionUp(int $expectedPound, int $positionsToMove): void
+    {
+        $prices = PriceList::fromList(
+            new Pound(1),
+            new Pound(2),
+            new Pound(3),
+            new Pound(4),
+            new Pound(5),
+            new Pound(6),
+            new Pound(7),
+            new Pound(8),
+            new Pound(9),
+            new Pound(10)
+        );
+
+        $this->assertEquals(new Pound($expectedPound), $prices->move($positionsToMove));
+    }
 }