Thanks everyone, the more I learn about the MFDB market the more it seems it's not going to be "cheap" for a while. The prices cited here are not bad, but I doubt they will go up--so I may have to bite the bullet and sell most of my rz system, which I rarely use.
It makes me feel sad ditching it, though. These are big, well-built lenses. And I'll inevitably use the money to buy a tamron zoom or something....