I'm not sure if your still following this thread but here is my .02 cents. I like all types of builds I actually went to Carlisle to buy a Cobra and it was pouring that day. I met Dan from IFG because he didn't have to cover his car when it rained and it reminded me how much I loved the styling of Lambo's. He talked me out of a Countach because of how hard it was to see out of them while driving and I bought a Diable VT. So to your question and I would think this would be for about any type of "kit" for a lack of better words would be to find out what it costs for the body, interior, motor, suspension, and other options which the manufacturer can help you with. Then the rest is up to your abilities. If you can do everything like fabing up mounts, welding, suspension, body work, painting etc then you can save a lot if money. Once you get a price for the vehicle you want you can add on 10K for a complete "kit" that has everything with it to probably 80K if it just has the basics with it. When I bought mine a Cobra was around 15K and you still needed a doner Mustang. My Lambo was about 12K delivered which was just a shell. The expensive things that you had to buy for it were wheels and tires, a Fiero doner, paint which was $2500 just to buy and tons of metal for framing plus all the small stuff.
So to sum it up after buying the "kit" and I am using that term because mine was a box full of parts, you can expect to add 10 to 80K depending on what you want to have when it is completed. The most important thing that you need more than money is patience.
Don't know if this helps
Thanks
Jim