Depends on the body, how much of the work you are going to do yourself, and what type of restoration you are talking about. I can tell you that I bought my '66 for $2,000, and I have put about $3,000 into it on interior and mechanical only (keep in mind this is only part costs, and I have done the labor). Now I am getting into the body, and I am guessing that is going to be another $4,000 for the bodywork and paint job.
If I were to do it over again I would have bought something that needed more mechanical work than body work (just because I feel more comfortable doing that stuff). Some key areas to check when you are buying one are the underside of the cowl (have to get on your back and look at the metal that comes out from the top of the firewall--65-66 are notorious for rust issues there), obviously the frame should not have rust issues, floor pans, and trunk floor pans.
If you are looking to make money on one of these things then I doubt you will. I will be lucky to break even on my little project. But, if you are looking to fulfill a childhood dream then who cares. I am kind of glad I didn't buy mine with everything done already. Gives you a different sense of pride.