Rust free Z cars are very tough to find, but it is well worth the effort in the long run. I paid $1,200 for a rusty 240 and ended up scraping it in the end. Ultimately found a rust free 260 project car and purchased that. Upon further inspection I found a botched collision repair that is going to set me back another $1,500 to repair.
The moral of this story: look the car over very well, put it on a lift and poke all around the floors, frames, quarters and rockers. You must factor in time and money for any necessary repairs, both have been the killers for me. Don't jump on the first Z you find, I guarantee it will be cheaper in the long run to pay a little more for a rust free car. Just my $0.02 though.