I bought a used Rolleiflex 3.5 F about 20 years ago for around $ 700. It has the Planar lens and has a working meter. Therefore, you could probably get a Rolleiflex with a Schneider Xenotar and non working meter for less than my type. The Xenotar is supposedly just as good as the Planar. Also, since I use a hand held meter I really didn't need a working meter on the camera.
If you want to go interchangeable lenses, the Mamiya 6's and 7's are supposedly very, very good. The price may be a little higher, though.
Fuji also made some good MF cameras also as the 645 and I think also a 6x6.
If you want to get into Med Format real cheap, Holga's can be bought new for around $ 50 or so to try it out without having a lot of money tied up. There may even be one like this with a better lens and body. Seagull used to make a 6x6 that was very reasonable, but for about the same price you could probably bet a used Yashica.
Basically a medium format camera is not all that different than a 35mm camera. Don't be intimidated. It's easy!
Shooting 645 is definitely a step up from 35mm. If you like square then 6x6 is the way to go. If you don't like square and are going to crop then you would be better off shooting 645 in my opinion.
If you like rectangles and want the best quality then 6x7 is what you want. The disadvantage to 6x7 is the bulk and weight. Another disadvantage to 6x7 is that some 645 cameras have autofocus, matrix metering, and auto film advance etc. if you like that kind of stuff.
Buy what you like and can afford and don't worry about the critics. After all it's all about the image, right?
Wow! I just answered this thread again without realizing it. I sure hope the OP has found a camera by now.
One significant, and often overlooked advantage, of the Mamiya TLRs is that they use a bellows focus. This is both an incredible blessing and a curse in that it allows ridiculous levels of close focus but the "curse" is that one needs to remember bellows factor. That being said I believe they made the right choice.
Maybe I missed a post: WHY you want to change from 35mm to MF ?
I guess because we ALL like large negatives.