Good luck finding a tough and reliable rangefinder for under $500. Especially if it needs service, and most will.
I love my Contax ii and I use mine regularly, but if you intend to go that way then be prepared to spend the money to have it overhauled. Henry Scherer did mine years ago and it is probably my most reliable rangefinder even yet today. The shutter is very good and mine has held up very, very well. I think the rangefinder itself is about as bulletproof as it can get and it is still dead on the money. But the overhaul certainly wasn't cheap, and I didn't get it back quick, but I do feel that it was worth it. Not everyone feels the same way and that is fine. It is a great camera though and the lenses are amazing.
I also shoot Barnack Leicas, and enjoy them, but they are not easy or fast to work with. Old rangefinders are just fiddly to use and do require the user to have some patience. I use them because I enjoy the experience. Like the Contax II, mine have been overhauled so they are pretty reliable, but that reliability costs money and the rangefinders do not stay aligned as well as the one on my Contax II.
Likewise my Bessa R rangefinders are nice cameras and you may get lucky and find one of those for around $500, but if you do I would have it checked out by a reliable tech. I last sent mine to Cosina a while back and had them clean it and service it. I am glad I did but, again, not cheap nor fast. In my humble opinion the rangefinder itself is the weak point on the Bessa cameras.
I loved my Leica M-A and used it a bunch. Great camera however, slowly but surely, the Contax ii and my Zeiss Ikon ZM took its' place and are now my regular user cameras. One caution, the rangefinder on the Zeiss Ikon also needs alignment occasionally. But again, I'm not sure that either of these cameras fit your price range.
Leica M cameras are great options but none of them are getting younger so you will need to consider service there as well. Fortunately there are options but neither Zeiss nor Leica techs work particularly cheap.
Even the Russian Kievs are good options and can run reliably for quite awhile if they have been serviced by reliable technicians. The potential wild card with any Russian camera is the build quality but a good one can cost you less than many of the other options.
If there is a common thread here it is the fact that all rangefinders, even new Leicas, will eventually need some attention, and that attention will usually be expensive. For most of them the weak point is usually the rangefinder itself. I think the Kiev and the Contax ii are the only possible exceptions in this regard.
That is why the single lens reflex, even the simple Pentax K1000, is often a more reliable option. It outlasted a lot of students and there are not a lot of rangefinders that can honestly make that claim.
EDIT - The Argus C3 might be the exception to the rule. It is not considered quite as sophisticated but it does take really good photographs if you do your part. It is also the only camera of any kind that I have been able to clean and repair without expensive, outside assistance.