There are still a lot of rubber bumper Bs around, rust free is certianly worth something, with a shot interior and the price of doing all that might be a good candidate for a donor tub.
I have noticed a lot of the rubber bumper cars have seemed to survive with less rust that the ealry cars, were they doing something bette for rust protection?
I would think in the under a grand range for the price, but some people will think they have a rare old car and a gold mine.