You can sometimes find a seller desperate for money, usually get good deals from them. The guy I bought mine from, a very nice man by the name of Brian, knew that it was a very clean body (still had just the original paint under a very light coat of primer), had a super nice Land Rover Series IIA in his garage and an FJ62 out front so needless to say he was an enthusiast. However, he needed the money badly for personal reasons and I got it for 1600 cash even though asking was 2000. I suppose it helps when you show up with a flowerstroke, a trailer, and are not suprised by what it needs and that it did have a small amount of rust.
Rust sucks but it's not the end of the world unless the frames rusted out, the body isn't salvagable, and there's not a single part worth saving. Anything approaching 35-40 years old is going to need rust repair unless it's already been done.
Edit: As far as that specific 40, the '74 in my sig has much more rust than that one (atleast from what I can see in the pictures) needing both rear quarters, rear doors, floors, and the rear sill and 1500 was paid for it. However, we knew it from the start and didn't mind given that I like to fabricate that stuff anyway. If you want to take a shot at learning sheetmetal repair and welding (if you don't already) then it could be a fun project. It could be more then you want to deal with at the current time though.
