If you really want a "normal" used Leica lens, look for a 40/2 Summicron C, or classic 50/2 or 50/2.8 collapsible, those cost the least, you should be able to get either for US 300, if you are patient.
Otherwise there are lots of good alternatives, foremost from Cosina Voigtlander.
I recommend to stay away from Russian lenses, unless you want to spend a lot of money and time trying, fixing, returning, etc. With exception, maybe of the Jupiter-12.
Roland.