428239 Submit A Form If They Have Paid For Credits. (php)

I need some script that will allow people to submit a form a certain number of times based on their order.. i.e. amount of money received from PayPal and possibily other payment processors. For example, a customer orders 1 article promotion so he is able to submit information of the article that he wants us to promote once. The next time this customer attempts to access the submission form, they are shown the "sales page" to order more article promotion credits. To avoid confusion, the form will not accept duplicate submissions on the URL (if the URL has been added previously, the submission fails and the credit to submit is NOT lost (it remains so they can try again). The customer can submit the form for the number of credits that they have paid for and when they run out of credits, they see the sales page. The sales page displays if they do not have any credits. Initially I want to get this idea working with payments processed through PayPal. It should be simple for someone who knows what they are doing. Any question? Ask. Skype or yahoo preferred for communication with successful bidder.