[Typo3] Anyone create a simple membership payment extension?

[Andrew Chew]

I am attempting to create a membership payment system to control paid  
member access.

Basically, I am planning on creating an automated system that adds  
Groups to a User's access list as a result of a transaction to  
Authorize.net (a payment gateway). The user could select from a list  
the levels of access and then charge their cc and get immediate  
access upon success.

Anyone know of an extension that could be modified?

Thanks, Andrew