Check your local Border's book store for a soft-cover 8.5x11 book by Motorbooks International titled "Chevrolet Corvette Restoration Guide" by Lindsay Porter. It's basically a picture book about restoring a 69, but has a nice 12-page section in the front about what to look for and checklists to use when inspecting a Corvette. C3's aren't a whole lot different than C2's, especially the chassis.
Basically you are looking for frame or birdcage rust and damage evidence, and fiberglass damage, plus originality and condition.
You first need to decide what you are looking for, a basic project car, a daily driver, a streetrod, a weekend shine & show, or a pristine original museum-quality original car with a pedigree of NCRS certifications.
Price fluctuates wildly with condition, originality, options, the naivety of the buyer, and the honesty of the seller. The general rule is that you can buy a better car than you can build for the same money, so if you want a project car, you'd best want it for the experience of doing a restoration or building a streetrod, not for saving money. If you aren't looking for a project, decide what level of quality will make you happy and don't settle for anything less.
Get familiar with the price ranges... it's a lot like real estate: the more you know about the neighborhood, the better you understand the values, and the less likely you are to get fleeced.
Look at a LOT of Corvettes very closely to educate yourself before you even think of buying (many make the mistake of falling in love with the first car they look at), try to get first-hand help from someone knowledgeable about C2's when you get serious.
BTW, sellers generally know much more about Corvettes (even if they play dumb) than first-time buyers, so don't expect to find any super bargains out there. And, verify anything a seller tells you about the car; you can't go back and complain that the seller said it was a "matching numbers original car with only 37,000 miles" when you discover that ain't so, 6 months later. Used car sales are as-is, where-is, buyer beware.
Have a look at this website for books and tapes about buying a Corvette (including the book I mentioned):
http://www.ncrs.org/store/shop.cgi/page=index.html