Thank you all very much.
When I say I am on a budget I mean I don't wish to spend more than $200-300 at this moment. I've already stretched my hobby budget by getting some lenses for my Canon F-1 and some darkroom equipment.
I like the idea of getting a TLR, probably some Yashica. I still need to read about other makes and models you recommended. I am not a big fan of getting a Pentax - they look to me like some over-sized 35mm cameras and I would prefer waist-level finder.
Also the square format of 6x6 appeals to me for some unexplainable subjective reason.
Dittos on everything John Wiegerink said. I have an Ikonta 521/16 with the Novar and it is really fun and easy to use, just fold it up and slip it into a pocket. Recently CLA'd, the shutter speeds are spot on. I also have the C33 with the 80, 105, 135 and 180 lenses. Image quality is outstanding with all of them. It's a bit heavy to carry around, but not something you can't get used to.
My suggestion to OP is to first decide the fundamental body type, which can take interchangeable lenses...
Single lens reflex
Twin lens reflex
In all three types there are mechanically timed shutter mechanisms
In the SLR there are electronically timed shutters in newer models in addition to mechanically timed shutters in older models.
The suggestions so far are all over the map, because the OP has not sufficient bounded the search parameters.
'Inexpensive' is not necessarily confined to much older cameras...You can get into a fairly modern SLR like the Bronica ETRS for about $300 with lens(es), about 10% of the new price 15 years ago.
I feel a bit overwhelmed. Having read all your suggestions and advice I think I will try to limit my preferences:
-I prefer either 6x6 or 645, with more preference for the square format of 6x6. My enlarger came with a 6x6 negative carrier and a 75mm lens, so I am ready.
-interchangeable lenses would be nice, but it is not that important, I think I will eventually get two medium format cameras - one with a fixed lens and another one with interchangeable lenses.
- my preferred style would be either TLR or a SLR with a waist level finder at the moment. Some rangefinders look lovely, but I want to depart from my 35mm/DSLR habits.
-I would prefer a model that is relatively easy and cheap to fix by a specialist. My own mechanical skills are limited and although I'd like to learn a bit about cleaning and fixing cameras, I am not gonna do it now.
-I have a Gossen Luna Pro light meter, so the camera does not have to have its own meter.
If you are lucky you may get Rolleicord V(x) for less than Euro 100. Good luck.
... then seriously consider the reccomendations for Rollei Va or Vb. That was my "starter MF camera" in 1982 and I used it until a couple of years ago when I got the uncontrollable urge for a Hasselblad. I tried a Yashica along the way and didn't like it as much as the Rolleicord. Plus, Rollei accessories are easily available so i fyou want to expand your capabilities you can do that... except you'll be restricted to a single lens, which did not turn out to be too much of a limitation for me.
Low cost + interchangeable lenses screams "Mamiya TLR" to me. See Mamiya C33, C220, C330 variants. I have some examples in my gallery of C330 with 80mm lens. I have some other lenses but to be honest I almost never take the 80mm off.
Though I must say, I occasionally see a Mamiya RB67 SLR with lens for under $200 on Craigslist. I don't own one (yet) but I imagine them to be a bit heavier than the C330. I could be wrong on that. As TLR's go I think the C330 is on the heavy side because it's a lot more complex than a Rollei or Yashica with non-removable lens.