I went to an antiques market in Des Moines today, and found this:
It's a Leica M6. It looks nice and clean, the battery cover and body cap are missing. The guy who sold it to me said it doesn't work, but the shutter seems to work on all speeds, and the winding mechanism seems OK too. I'll need to get the missing bits and a lens so I can test it.
Oh, yes, I paid $12 - that's twelve dollars - for it :)