This is a slightly odd requirement, so it may not work quite properly, however I think in theory it should work.
Edit the normal Student role, to take away the 'Review my own attempts' capability. Also, edit all your quizzes, to get rid of all the "Immediately after the attempt" review options.
Then create a new Paid student role. Give that the 'Review my own attempts' capability.
Make sure that when students self-enrol in the course, give them the Student role. When they pay, give them the Paid student role in addition to the Student role.
As I say, in theory that should work, but there may be some issues, because it is an unusual set-up.