There ar emany different kits out there. Some you have to use a donor car and others you don't. Regardless of what kit you decide on, let me give you a rule of thumb as far as cost. Whatever you pay for the kit, expect to double that figure wwhen you add in all the items that don't come with the kit.
I am in the process of building an A&C Kit and so far no real problems. Visit their site and check out their produc
http://acautos.com/
Good luck with whatever kit you decide on, and don't be afraid to ask questions. In here, everyone is very helpful, it's like a brotherhood of Cobra builders/owners.
Tony