Vendor Rebate for Janitorial/Industrial Paper

I am working with a prospect with a requirement to handle rebates from vendors on a monthly basis. The rebate is based on the number of cases of product sold to a specific customer during the month. The customer is invoiced for an amount equal to the price less the rebate. The sale price is often less than the cost. I am looking for a solution that would handle this at the time of customer invoice, adjusting the cost by the rebate amount. Any suggestions would be greatly appreciated.

Hi Tom Did you get any response to this or did you find a solution?