I bought my 72 240z for $500 in 2000. It has very little rust, a 5-speed, complete interior, curr. tags, and it ran good. It had a fuel leak ( oh yeah, it also came with dual webbers) I've been driving it pretty much everyday since I bought it with very little demand from the car.
I'm confident this car is solid and ready for some real mods.
My opinion is to try autotrader.com and do a search under collector cars in your area. I'm sure you could find a good project car and maybe even one that is in pretty descent shape for that price range. Good Luck