No need to worry about brands. There are only three, FED, Zorki and Kiev. No need to worry about lens mount. There are only two, Leica and Contax. FED and Zorki are Leica mount. Kiev is Contax mount. There are no Leica mount Kievs and you are not likely to ever see a Contax mount FED.
I wouldn't worry about price either. eBay will show you a fair indication of price. $30 should get you the camera you need and, for starters at least, you should definitely not pay $50 for one.
As far as choice lenses goes, Leica mount wins. A greater range and variety is available in Leica mount. Further, the most common Kiev lens, the Jupiter-8 f2 50mm, is also the most common lens on a Zorki i.e. it was made on both Contax and Leica mount. A very cheap but very noteworthy lens, the Industar-61LD, was never made for Kiev. While the original Contax had a collapsible lens, no collapsible was made for the Kiev.
I could get flamed for this but I suspect that Kievs are not as reliable as FEDs or Zorkis. This is because the camera it was copied from, the Contax was more complicated than the Leica and thus by its very nature imposed more quality control problems. Kievs are a bit famous for arriving dead, new out-of-the-box and are not so easy to fix as a FED.
Being somewhat biased, as the owner of a Zorki-6 and a FED-1, I would recommend the Leica type over the Contax type. In addition to the above, the Kiev is a much larger camera, and offers nothing for its extra bulk.
The Zorki-6 is a thoroughly practical plain-vanilla shooter, the most practical FSU of all, and this is reflected in its price. You don't see them selling for $15. Because it is the only FSU to have a hinged back door and it still has the film-grabbing claw like the old bold bottom loaders, it has to be the easiest-loading 35mm camera ever made, anywhere. They usually come with an f3.5 Industar but are also available with the f2 Jupiter-8. My Industar is a good sharp lens.
I got a FED-1 because because it so compact and so elegant. I would recommend a FED-2. It is almost as elegant, almost as compact, is usually cheaper, and it has flash sync. More modern FEDs and Zorkis have slow shutter speeds. I don't consider this to be an asset.
I'm not familiar with them but the ugly-ugly FED-5 has to be worth consideration. When sellers claim them to be brand new in box they often really mean it. This must have cosmetic merit, at least.
Stay away from any Zorki higher than "6" and any FED higher than "5"
Hope this little ramble helps
