Apply Expenses against an Invoice (Profit per Job)

Hanz

I would like the ability to somehow "relate" or "link" Expense Transactions to a specific Invoice, so that we could see our profit on that specific service rendered. For example, as a Contractor, if I purchase materials for a Job, and also hire a sub-contractor to perform the labor, then I should be able to "relate" the Expense Transaction for the Material Purchase & the Expense Transaction for the sub-contractor (vendor), to the Invoice. Not only to see profits per job, but to better describe how the funds from that project were utilized.
I would love to pull a report with all of my invoices individually listed, with columns showing revenue, cost, and profit for each.

Note: I notice the Transactions feature that allows you to tag a Customer or a Vendor. I have not been able to see how this feature is useful at all. Customer & Vendor aren't even available fields to filter your Transactions list by.