Paypal IPN or API, PHP & MySQL Update database with multi elements including accounts, passwords, MISC, Receipt info default.
I have done a few payment systems for a MMORPG i work for, I can simply show you or my old website has it also.
Payments systems are easy ad mines almost already made, suggestion using IPN for Paypal much easier to work with like Plimus.
You tell me the table fields or you want me to make one?
List the info you think i might need to be provided prior to starting the work It will be done when you tell me what i need to know.
Looking forward to working with you in the future as well as on this project.