Hi there.
Ive had 3 500`s ,now down to 2, they were all basket cases, but with a lot of passion, enthusiasm and sheet metal work know how, does help. Alot of basket cases go for around £1000; average condition cars which work but need TLC probably up to £4000, and good ones .....well as the previous posts have indicated, up up up.
The round speedo version is a tad more desirable, ie the F or the R, whereas the L is the long speedo with plastic dash , but conversion to a round speedo isnt too hard to change.
If you were to get a poorly car, expect to put new floors/inner/outer sills, etc, but at the end of the resto you`ll have a great car. Mike.