[Three Peaks]

As stated before, your best bet is going to be to keep your eyes open for an unfinished kit and make an offer on it. I've seen them come up very cheaply at times and often you get the kit with a number of additional items like engine, tranny, rear end, wiring harnesses, etc... that would be extra otherwise.
If you find a Factory Five kit, you can save a bunch of money by buying a wrecked Mustang and using all the donor parts the kit is designed to use.

In any case, you'll be into the car at least $20 K by time you get done even with the best of intentions and great deals on parts. Depends a lot on how good of a shopper you are and if you are mechanically astute enough to be able to use everything you can pick up cheaply, or refurbished parts you can do yourself.

Good luck on your quest. Don't think building from scratch will be any real savings either. By time you get done you won't have any real savings at all- I know this from experience.

Bob