Coupon system for PayPal payment

Hi, We need a coupon system for [login to view URL] . The site does not have a shopping cart-system at the moment. A WordPress template has been used. The job needs: * Create 1000 unique coupons * Transform the current check-out system at [login to view URL] to include the possibility to type in a coupon. * If the coupon matches one of the 1000 unique coupons, the price should be reduced. * Once PayPal (our payment provider) has accepted the payment, the coupon should be removed from our system. * No design is required, but compatibility with our existing template is requirement. Feel free to come up with a system architecture. Our idea is to put the codes in a SQL-database and then use PHP to query the database. However, we do not know how to acknowledge that the PayPal payment has been processed. This should be a rather small project for someone experienced in the field. Please write an estimation for hours and your hourly rate. Also please share some references of prior projects that are similar to this. Regards, obby