There are about a million threads on this site on how to buy a used Cobra. Take some time to read a few. Start with
Mr. Mustang's "how to buy a used Cobra" thread.
There are so many different manufacturers of Cobra replicas, and so many variables when it comes to a used car, that my advice would be to 1) educate yourself about the different brands and 2) take your time finding the right car.
You should also check out the "for sale" section on this forum as well as
www.cobracountry.com for a large selection of cars.
Good luck in your hunt.