How to add cost to a product?

How to add cost to a product?

Hi there...in the CRM products, let's say I sell something that costs $100, but my actual cost of that is $85 (15% margin).  How can Zoho handle that?

What I am seeking is to have a salesperson add in the cost to the customer so that it shows $100 in invoices, etc, but internally, I know that I made $15 in gross margin off of the transaction.

Thanks!