Add Vendor Rebate Option

I would like an option to have a vendor rebate be selected. So, a customer might qualify to get a phone for $49.99 but MSRP is $629.99. Customer only owes $49.99 and then the Vendor I got the phone from will pay me $580. And in another scenario. A customer will do an AT&T plan, I make X amount from AT&T for doing transaction, the customer doesn't pay me that, but the vendor does, so I would map that to the vendor account to mark it as waiting to be paid.