I've been selling my gear off and was thinking what sort of budget kit might be kept "just for fun". My FD 135 2.5 is a no brainer for a tele: cheap, and has wonderful IQ. I looked at some negs from an old Helios that I'd put on a Canon FT QL w/ an adapter, and that made my decision for a 50 lens (or a 58 actually). It's remarkable how nice a kit you can put together for under $100.
Here's the Canon, and the link below it is to some shots from that Helios. I've always appreciated Russian glass on rangefinders, but their SLR lenses are just as good.