You're probably better off trying to find an Bronica SQ-A/Ai/B kit(body+viewfinder+120 back) rather than put together separate parts. Things like WLFs and 120 backs for the SQ series have really jumped in price, so while bodies and lenses(e.g., the 80/2.8 and 150/3.5 or 4)are reasonably priced, you may actually spend less for a kit. I shopped for a long time before I recently found a NOS 120 back at a good price. I'd avoid the SQ-Am--blow the motor drive and the whole camera's dead. Overall, Bronica SQs, because they're really the only 6x6 SLR outside Hasselblad, have actually gone up in price since I bought into the system in early '09.
Originally Posted by wilfbiffherb
For the money, though, you might also look into the Mamiya RB67, preferably the later ProS or ProSD bodies. Hands down, the biggest negative for the $ on offer right now.