Billable Expense "markup"

Billable Expense "markup"

I order parts for my customers and "resell" them once in a while.  Although the expense bill to customer is cool, it doesn't account for my time or any markup, or interest I might pay on that product before the client actually pays.  It would be nice if there was a way to edit the expense such that I could apply a "markup". 

Thanks!

Sean Garland
Garland Tech, Inc.