$350 sounds like a lot for an RB-67. I feel that used pro gear CAN be a good bargain if it was used properly and cared for. At my level of usage, high mileage gear in good shape could have a lot of life left in it, but for professional use it might be shot.
On a related topic, I recently bought a Mamiya 645 1000S. What is the proper series of Mamiya lenses for this camera. I'm becoming confused! I received an 80 and 45mm with the kit and would like to add a 150 or 210mm.