My vote for "cheapest, best vintage MF" would be some of the old folders, with a early Yashica TLR a very close second. Of course it depends on what you mean by "really solid photos". I'll assume you mean more than a box camera or Holga.
Agfa Isolettes (
http://www.rolandandcaroline.co.uk/isolettei/isolettei.html) are under $30 and even old Zeiss-Ikon 6x6 folders with Novar lenses can be found close to $30. The problem is finding one that is known to be working. Big issues are bellows (cracked and leaking light), shutters, and (on the Agfa) stuck focusing rings. But all of these can be reasonable home repairs except for bellows that are truly shredded and there is "how-to" info on the web.
You can often find these very cheap on eBay, but it's a bit of a crapshoot as to condition and the shipping can cost you more than the camera. Rarely have they been tested, so my view is that you need to buy 2 or 3 to get or assemble 1 that works. There are sellers who has tested them or restored them - but then you're likely to be well over your $30 limit).
I recently bought a cheap Agfa Isolette and spent about an hour cleaning and unsticking the lens. Shutter seems OK - will know when I develop film tonight. End result is over $30 if I place any value at all on my time - but it was more fun than cleaning the basement.
Here's something to consider that I saw a bit ago:
http://www.nwcollectorcamera.com/zeiss/ikonta_b.htm
I've never dealt with them, but it provides a reference point.
A TLR can avoid some of these issues. But with these simple folders a crude lens cleaning is within reach of the typical user - not necessarily so with the TLR.
Anyway, that's my 2 cents.