prestashop developer needed

I need some changes to an existing website. I need you to integrate cash reward system in it so that when a person buys something from my site, they can get some points that they can later redeem. My max budget is 100$ so will prefer someone who can do it in less than that because there are many add ons that can do this work. its just a matter of you integrating it in my site and making it work the way i want to.