Credit Based Download System

I am looking to build a cart shopping system based on credits (for example <[login to view URL]>) People will add "credits" to there shopping cart, then they will be taken to a order form (through payment gatway - e.g [login to view URL]) after which they get returened to the site - credits are added to there account and they can now download files (1 file = 1 credit). Download links after an order must only be active for up to 30 minutes where after the link will not work any more. ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Deliverables must be in ready-to-run condition, as follows (depending on the nature of the deliverables): a) For web sites or other server-side deliverables intended to only ever exist in one place in the Buyer's environment--Deliverables must be installed by the Seller in ready-to-run condition in the Buyer's environment. b) For all others including desktop software or software the buyer intends to distribute: A software installation package that will install the software in ready-to-run condition on the platform(s) specified in this bid request. 3) All deliverables will be considered "work made for hire" under U.S. Copyright law. Buyer will receive exclusive and complete copyrights to all work purchased. (No GPL, GNU, 3rd party components, etc. unless all copyright ramifications are explained AND AGREED TO by the buyer on the site per the coder's Seller Legal Agreement). ## Platform Running on a Unix System PHP MySQL