Some great suggestions here already.
I'll second the suggestions for the Retina IIa or Zeiss Ikon Contina. The Contina's a little more fiddly to use, but both are sturdy, well made and feature great lenses. They're also small.
Similarly, you could do well with an Agfa Karat IV or Agfa Karat 36 (or an Ansco Karomat, which is a re-branded Karat 36). Again... well made and with great lenses.
I'll also second FSU cameras provided they come from a reputable source like Oleg or Fedka. A Zorki 4 or 6 with a collapsible 50mm industar or FED lens could fit the bill very nicely.
If you don't mind the larger size of fixed-lens Japanese RFs from the 50s, they're pretty much all good and all inexpensive. Konica III, for example, is a great camera. I have a Petri 1.9 Color Corrected Super (a $10 flea market find) that is absolutely fantastic.
Lastly, if you want to shoot 120, a Seagull 203 or an Iskra in good condition would make a great coat pocket camera. They can both be a little rough around the edges, but they're both small and they both take good pictures. For a step up in 120, look for a Konica Pearl III.
All of the above can be found for under $100 if you're patient.