A lot depends on what you want to do with it. In particular, do you need to be able to shoot fast, or do you have plenty of time and do you need interchangable lenses. Also Medium format is actually a whole group of formats that just happen to use the same film, so you need to decide which you want. I use an RB67 for most of my Medium format work and they can now be got used remarkably cheaply, but it isn't quick to use. I have just bought a Pentax 67II for use in the air and it has been a revolution. That wasn't cheap, but you can pick up the older model fairly cheaply.
David.