Probably the only way to find out for sure is to auction it off on eBay with
a lot of pictures, warts and all.

In lieu of that, do some research on eBay to see what recent cars have been
bringing (or not bringing, depending on the seller's reserve or the
buyers that
were looking during the week it was on eBay).

You didn't say what transmission or differential you have, or the HP of
the original
engine, or what options the car has.
The originality of every part on the car will be important to some
buyers, as will
evidence of past collision damage, any corrosion, and the quality of the
paint
and chrome finishes.

Special performance or amenity options can make a huge difference in prices.
Considering that a recently-restored example with few options can bring
$45k+,
buyers will be comparing your car to cars with new paint, top, upholstery,
flawless frame, new rubber, etc, etc and deciding if they want to buy
your project
or spend the money upfront to buy a creampuff they can enjoy driving
from day 1.

A really rough guess would be $30k as it sits, with the original engine.
Might be worth
your while to get the work completed (and price it accordingly), since
that will make
it attractive to more buyers, especially if they can drive it before buying.

If you have an eBay sign-on, here's a link that shows some
recently-completed
auctions of 1966 Vettes, many of which did not sell:
   http://tinyurl.com/2vtuqv

I'll give you $1,500 for it.  =)