The Contax is a superb camera and very cheap.
All the major digital backs will fit the Contax 645, that's the good news.
I had one more than a year ago and loved it. But I hate tether and finally opted for not using MF anymore because of that (unless in a special config with a light Cambo or http://www.hartblei.de/
that I love the concept-design but have other priorities to fullfill today before).
But that I know, correct me if I'm wrong, Contax has closed the door forever and is unfortunatly a past story. No company has taken over.