I just checked the blue book for a '94 cobra. I think it was about $8,800.
I live in a place with nice dry air, but if I were looking in any other place, my first concern would be rust.
Most 90's cars have not had a chance to pick up too much, but back in the day, I bought a rusty '67 GT and repaired it badly. At the time I did not have the money or equipment to fix it properly, but now I realize that car was a bad investment because the money and time required to fix it the right way was much more than the ammount I would have had to pay for a rust free example.
You should be picky because these cars are available in good condition with reasonable mileage. I think the prices are starting to bottom out for the 5.0's because a plain Jane 60's car with a v8 will fetch $5,000 if it isn't too badly beaten up. A low mileage origional K code GT will bring more than $20,000, probably more than $30,000. Money you spend now to get the best example you can find should pay off pretty quickly if you keep it nice.
If you just want a driver, or a race car, get the best deal you can find.