skip260z

Rust is the number 1 issue. Even if it looks great, rust could be lurking deep in the inner panels or "frame rails." Get it on a lift at a body shop. Number 2 issue is Previous Owner hacks.. If the PO heavily modded the car, you could have a tough time trying to figure out their engineering vis-vis any Haynes, Chilton, or FSM. Get to know a good mechanic that can fly by the seat of his pants. Lastly and before all else, find a Borders or Barnes&Noble in your area and see if they have Wick Humble's "How to restore your Datsun 240Z" book... If you are dead serious, buy it, else - at least sit and read the first chapter in the book. Read and heed his words of wisdom and be careful what you wish for.

Take your car to several shops for an estimate on the repairs. I say several so that you can reduce the chance of being taken, plus you'll get an idea of prices. It all depends on what you are willing to spend for what you want to acheive.