data tracking for Wireless ISP

Overview: I imagine this is already done, but I own a wireless ISP and would like a webpage interface which query's paypal and grants new customers access to my network. Once accepted I would like them to have free internal connectivity between each other but when they leave my internal network I would like it to count towards their data cap. Website with paypal integration: I would like initial customers to be forced onto an internal website which will prompt for credit card details. That webpage will query paypal, and if the transaction is accepted it will add their username/password into Active Directory (their account will expire the following month by default). Background information: When they log in to a wireless access point, the AP will query through RADIUS their username/password and If they have data left they will be allowed to access the network. Background information: Once on the network they will be able to share files between each other for free but when they download/upload anything external on the internet it will subtract from the amount of data they were issued. Data Counter: I imagine a separate program will be required to count the user data as it leaves the network (so they may be required to login twice, once at the access point to get on the network and again at an upstream data counter) Website will need to query AD for data usage: They will also need oversite on how much data they have used so if they login to the webpage a data usage page displaying account information should be available. Account destruction: If they run out of data or the account expires, their account will be removed from active directory. If they add credit to their account before the month expires, an extra month plus a given amount of data should be added to their current account Summary: So i essentially need a website to query paypal then add a username/password to active directory with an extended field for data usage. I need counting software to subtract that data usage when that packet leaves the network. I'm guessing this isn't reinventing the wheel so i am totally open to any advice on alternative methods to run it Cheers Alex Miller