Welcome to the RF world!
IMO, the first choice is to decide if you want a fixed or (and?) interchangeable lenses camera. Then there are options.
For fixed, the Canonet GIII is an excellent one (shutter priority), the Yashica Electro 35 is another nice camera (aperture priority), and there are many others priced within a fraction of your USD 600 budget. So, it will allow you to buy other things.
For interchangeable lenses, I guess you would think about the "future", it is to find a camera able to "grow" with your expectations.
Any camera with Leica M mount (Leica, Leica CL, Voigtländer Bessa, Zeiss Ikon ZM) will do, and perhaps the only within your budget is the CV Bessa.
Another option is to jump into FSU gear. No M mount here, just two options:
LTM (Leica Thread Mount - 39 mm) or Contax/Kiev mount (bayonet - compatible with itself only).
Cameras in this range would go for as little as USD 50 to 200 depending on condition, accesories, etc. You can find a Fed ( models 2; 3; 4) or Zorki (4 or 4k with winding lever) and save a lot of money to buy lenses, either russian or Leitz made. Besides, there are lots of good and cheap lenses for really damn low prices (I payed less than USD 30 for a russian Jupiter 11 - 135mm f4).
Even being myself a Contax/Kiev addict (and those are excellent and fun to use cameras), I wouldn´t recommend them for starting, just because it´s mount doesn´t allow you to use any other lenses other than those made specially for them, and there are no adapters nor anyone is making newer lenses.
Good luck with your choice (and take care of GAS).
Ernesto