It's really not that bad, better than mine. With a few ounces of POR15 or Rustbullet and a small brush, the rust can be stopped before it begins to infect structure. The rusted areas can be fixed later whenever time/finance becomes available. Most of the people who sell Zs in condition like this for a low value because they believe rust is going to get a lot worse within one year. With technology like RustBullet or POR15, it doesn't have to get worse, especially if the car doesn't see rain. Rust is stopped first, then find some time to fix it.
http://www.rustbullet.com/
The shell of my 260Z that is being build is coated inside out with this stuff.
The coating is very tough. When I scratch the coating with my fingernail it doesn't feel like the fingernail has digged in at all. It the same kind of feeling you get when you try to scratch glassware with fingernails, very hard and slick.