Jesse from the Guru Team here.
Currently by default Shopify does not have a field that would contain your value for cost of goods.
There is an existing feature request for the ability to track COG without an app which I have upvoted and added our conversation here as a use case.
Merchants looking to track COG would need to use something like https://apps.shopify.com/profiteer-cost-of-goods-sold
In addtion we have a general guide on how to show VAT prices when applicable that may be of interest to you:
Feel free to reach out at any time if you have any other questions.