Shopify does not provide tracking for cost of goods sold (CSGS). An app is needed to add that funtionality to your store, unless you are ok to use Excel and do it manually.
You can try SimplyCost. It lets you add COGS to your variants and report stock/inventory value.
I am the developer of the app. It comes with 14 days trial.
This post is out of date, but the merchants looking at the same solution can use Merchbees Inventory Value.
Merchbees Inventory Value provides the total value of all items in stock in real-time. Whenever you click the report, you can always see the up-to-date stock value, no waiting!
And... FREE now! You can find more details on our app page.
If you have any questions, please don't hesitate to reach out to us at email@example.com.