I offer to build it for them, give them my contracting rates, and hope it works out for the best for them. If they really are passionate about it, they will be

I offer to build it for them, give them my contracting rates, and hope it works out for the best for them. If they really are passionate about it, they will be willing to pay to have it built. Maybe you give them a cheaper rate, maybe not. But if they aren't willing to put a couple grand behind it, then they should stop pitching it.