Closeup pictures of the rust would be helpful. A little rust may or may not be "just a little". Have you lifted up the floor soundproofing?
the price guides in the autotrader etc. should give a ball park - check ebay for completed sales and if you do a search on this forum there is lots of info on pricing.
other info like "matching numbers, how original, airconditioning, hardtop, condition of everything else etc." would help.