Canon QL19/QL17 (not the GIII). IMO much sharper lenses than the 40mm on the GIII (45mm 1.9 or 1.7). Does not command high prices at all.
Konica Auto S2. Another 45mm lens. Extremely sharp and the viewfinder has better brightlines than Leica (brighter, and corrected for parallax in both dimensions: movement AND size).
Minolta Hi-Matic 7s. Another 45mm from the same era. A bitingly sharp lens.
I never got along with the Yashica Electros either. They look pretty and the lenses are good, but I dunno.
Retinas are another good option with wonderful lenses. $50 for a working one might be pushing it though. Not as easy to right off the bat for the beginner, but not hard to get used to after some practice.
For under $50 most of these will need at least a viewfinder cleaning and probably light seals unless you get lucky.