The cheapest thing to do is find an amateur partner. That's also the most difficult.
If you want to get back into doing Pro/Am, then you should shop around and check out all the studios in your area -- not just the local AM and FA studios. Independent studios often have better teachers and lower prices. You really do have to check around to see what teachers you like, what their lesson and competition costs are, and what their availability is.
Another idea if you're willing to try group classes is to see if there's a local college team that allows non-students to join. The students in these group lessons are usually highly motivated, so it won't necessarily be your typical group class experience. And don't worry about any age gap -- if the team allows non-students to join their classes, then you won't be the only post-college person there.
Another source of decent group lessons is to check around and see if any studio has an adult dancesport program. These tend to attract more serious students and so once again might be a better experience than you've had in group classes in the past. And, as alway, you can and should shop around. Take a class as a drop-in, or just go and observe one night before joining.
