Incentive Based Website Design

I am looking to build a PHP script (or something similar) into a website. The script will be used to track logged in users who follow a link in my website and make a purchase on another website. I will be paid a percentage of the sales and will be returning a percentage the user who made the purchase (similar to coupon chief, Upromise, ebates, etc.). I would like something customizable that will allow me to easily add new links and also put in the percentages that I will pay the users so that it automatically calculates the amount owed to that user (so that I do not have to marry spreadsheets or manually go through sales reports).