In other words what Lurch is saying is that your question is very general and it's almost impossible to provide a specific answer. Photos can hide a lot of issues and we don't have any photos of the underside, or the most common rust areas, battery tray, chassis rails, floor pans, rockers, wheel arch, rear hatch slam panel, fuel filler area, lower front fender and behind it. Getting registered also means looking at bushes, suspension, brakes, motor (is it smokey etc..) - all of which cannot be tested from the comfort of our lounge.
Basically you have to buy a 240z like this expecting to find rust in these common areas, unless it's been restored 'correctly' which many have not (bit of bog and she'll be right).
If you're not willing to fix these kind of issues, I'd suggest looking for a more complete example (which generally go for $20K + now). But even then there is no guarantee's (unless you see documented photographic evidence of repair process!).
Of course you might get lucky with this car and find it has minimal rust / body rot, but only way to know for sure is inspect, take lots of photos and ideally have it put on a hoist so you can see the underside of it.
If you can't go personally make sure whoever does is familiar with these cars and will give you a detailed report.
All the best.