I can tell you that first, the 645 Mamiya lenses are wonderful, secondly, they are all now very, very inexpensive. I'm not sure why but that's the market right now. Again, Mamiya is just wonderful glass. Please think about one of their finest lenses, the 120 f/4 marco. This is one that will cost a bit more, KEH has it for about $500 but I purchased a perfect copy for $270 on that auction site. It's an amazing macro and portrait lens. l
Don't worry about the mamiya glass one bit.