User Registration or Security Assist

I am working on a site for a client. We are employing PowerCMS 2 and we also have the User Registration Solution Pack and Security Assist.

The client is a non-profit with web pages that should only be accessible to paid members. The desired process is to have new/renewing members pay via Paypal, then have the organization's treasurer take those transactions and update the members online via a MySQL interface (presumably via URSP or SA2). Based on this model, which product would be best to implement?

I'm thinking URSP might be overkillsince AFAIK there's no direct way to pay via Paypal and have that create an account in URSP, right? Plus since everything must go through Paypal first, having a user registration system would not be useful because no one would be allowed access without a payment. I'm a little fuzzy on the capabilities - This is my first time using either product. I could use some help with clarity here ... any advice you can offer is appreciated.