You might consider watching sales of Z's to get an idea of current value. Check Ebay for a week and you will have a pretty good idea of current avg prices by model and condition. $5k should buy a nice Z, and $10 a great one. Awesome = $$$.
Just about anything on a Z is fixable, but some are too far gone because of rust and make better parts cars than restoration projects.
If you let people know what your plans are for the car (reliable DD, high performance street, track, etc.) they will probably jump in.