Beware of the addictive potential.

Low: Japanese fixed-lens rangefinders from the 70s (Yashica Electro, Minolta Hi-Matic, etc.) or Soviet rangefinders (with all the complexities and weirdnesses thereunto appertaining). The Japanese cameras can be *very* good, but they generally aren't optimized for manual control, you have the restriction of a fixed lens, and repairs are generally impractical. I used to do a fair amount of street shooting with a Minolta Hi-Matic 7s.

Medium: There's not actually much in this range that I can think of. You might find a Voigtlaender Bessa-R (Leica-compatible screw mount) under $200; it's an excellent camera at the price point. Some plastic in the construction, rangefinder base only medium, and no automated bells and whistles. But you have to buy lenses, and your $100-200 will burn up mighty quickly on those.

High: Leica, obviously, but at a lower price point there are the new/recent Voigtlaender cameras and a whole line of lenses. You could go in for the old Zeiss Contax rangefinders---I think the 50/1.5 Sonnar is my single favorite 35mm lens on the planet. I don't know much about the modern Contax cameras. There are some very good medium-format rangefinders, but your profile says 35mm...

-NT