Risalinas …
First off, welcome to the club!
Lots of good advice above, especially going to meet with the local Cobra owners in your area.
Also, take a look through Cobra Country
http://www.cobracountry.com/home2.html
That will give you an idea of what's out there and how much cars are going for. It will be more expensive to have one built than to buy one that is already done, depends on what you are after. There is also the Cobra County Buyer's Guide, if you want a book to read.
Happy Hunting!