From what I've heard, Youxin is probably the cheapest of the Big Three--but his service is top-notch, he serviced my M3 and it's worked well ever since (and he even replaced the vulcanite gratis). He also used to be the fastest in terms of getting your camera back to you, although I think that nowadays his turnaround times are getting closer to the others.
You might also get in touch with KEH. They have a pretty extensive repair service, and are probably quite experienced with Leicas I would believe.