Jim, I think me and you need to have an email discussion, our minds seem to go the same direction as far as a custom build is concerned.
As far as an eco kit car, I don't think the ones that are produced would be within anyone's realistic budget, the few I've seen are $16,000 or so PLUS a Miata or similar donor car.
Have you checked out
CAD Product Design Consultant | DIY Product Design and Development | Robert Q Riley Enterprises ?