Membership/Subscription Addition

Here is my question – I am running a premium theme that I did not create, although I have modified many aspects of the site. I already have a “membership” part of the site. A user will sign up and choose which role they are signing up for (there are only two roles to choose from). The problem I am running into is adding a payment part for only ONE of the roles. So if the user chooses say role 1 – nothing happens, they just register like normal and when they choose role 2 – they get sent to paypal fill out the form for the subscription to the site and then once paid they are good to go.

I havent found anything really simple like that – everything I find includes all these features that I dont need.

Any suggestions would be helpful, I am kind of stuck and searching and testing would go faster with some other brains in the mix!

Appreciate any help!