Cheap is relative I guess. And everyone has their idea of what is cheap. $39 for a Polaroid back to me is cheap. Considering that the ones for my Bronica are $50+ USD, and I've seen them for some of my other cameras that go for $80-200.
For me, it would be related to what a standard film back costs vs the back+shipping vs how much use I'd get from it vs the cost of a Land Camera itself.
When it comes to Hasselblad stuff, it's always a bit expensive because it's good quality and the name carries weight. So I'd expect more money for the same kind of product then a Bronica back that does the same thing. And so on.
Anyway... GarageBoy, have we helped here? Maybe if you give more details on what exactly you hope to accomplish with the camera(s), your intended usage, what you'd like from it etc will help us aim you more in the right direction?
I don't know where you are located but I will be happy to keep my eye out for things for people here locally if I come across it and it's within the price range you want. I've found cameras and film for people before a few times.