Merchant Affiliate Program

Hi,
I was building a PayPal Shopping Cart with the PayPal Integration Guide and completed it after four months. To my horror, there is no affiliate tracking system that can be built with the integration guide. However, I don't want to buy and start all over with a new shopping cart again, after spending so many months to build it.

(a) Is there any available off-the-shelf Affiliate Tracking System that works in conjunction PayPal Shopping Carts already developed with PayPal Integration Guides? I want to continue using my shopping cart developed with the PayPal Integration Guide, and just want a reliable affiliate tracking system add-on.

(b) Secondly, if your answer to (a) is "yes", are they associated with a monthly or annual recurring fees?

(c) Thirdly, are they [affiliate tracking system] licensed to only one domain, so multiple domains require multiple licenses to be bought?

Anyone has any ideas how to get affiliate system add-ons ??? Affiliates are needed to boost sales level. Without them, even a nicely built website can't generate much business for one.

Regards,
Paul