You likely should buy a camera that has been serviced, because at this point, nearly any camera will need some attention.
The older folding cameras will need to have shutters, lenses and viewfinders cleaned, while Japanese cameras will need new light seals, if they have them.
Of course, this often raises the price.
Next, the format: 6x4.5, 6x6 or 6x9. Certainly, each has its merits, and if we all had unlimited cash, we could buy one of each. Keep in mind that some cameras are dual format, either by flipping a lever or by inserting a mask into the film chamber.
With your budget, you could afford a Zeiss Ikonta 6x4.5 or 6x6 or a Mess Ikonta 6x6 (524/16), which has an uncoupled rangefinder. You would want the one with a Tessar lens.
You probably could pick up a nice Agfa Isolette III with an uncoupled rangefinder and either an Apotar or a Solinar (the better lens). You definitely want one of the models with leather bellows and that has been serviced.
There are classic Voigtlander Bessa 6x6 models with a Vaskar (triplet) or Skopar (four-element) lens within your price range.