I have and have had many rangefinders, including Leica, I used a M2 and M3 while in the Air Force and bought a IIIG but found that the Canon 7 or 7s while may not be as well made was overall more functional. True the screw mount lens are not as quick to change as a bayonet but not too slow as to be unusable and the Canon is easer to load. Canon lens are excellent, so either a Canon P or 7 is well worth considering if you find one in good repair.
I was given a Retina III C big in 1965 while still in high school, still have it. Retinas have a different DNA than other rangefinders, the rangefinder does not couple with the front lens elements for the 80 or 35mm, has the interlock shutter aperture combo, the light meter is not coupled to the lens, but the standard 50mm 2.0 is a great lens. The camera has a good feel, meters in EVs, change the shutter speed and the aperture is locked to the shutter and is adjusted automatically. I know of some who took the interlock off, the just hated it. Folds up nicely. The IIIS has true interchangeable lens but is not a folder has many of the same quirks of the III C, and lens are somewhat slow, one of the reasons to own a rangefinder is fast glass. If you are up to learning the oddities of Retina, you may want to look into a Retina II or III.
For fixed lens rangefinders there are many with excellent lens, Olympus RC, Konica S3, Canon QL 1.7 to name just a few.
I have not owned a Russian copy, Federal or Contex copy, the few that I have handled did not impress me, others seem to like theirs.
Bessa's seem to be well liked, both the screw mount and M mount versions. Good selection of lens, known for wides.
In terms of price and value I would start with a fixed lens rangefinder with a good quality fast lens like the Konica S3 or Canon QL 1.7, if you like using it then consider selling the kidney for a Leica.
And if you are selling body parts for your habit, then you might want to look at a Konica Hextar M, uses M mount glass, takes up to a 135, built in 2 FPS winder, 1/2000 shutter, and the Konica 50mm is an excellent lens, set you back more than a Leica.