Everyone thinks they can build things much cheaper, but few succeed because the reality is that if you COULD actually build for those prices, local contractors would be doing so and making $$$.
Good luck building a finished house in Cypress Dunes for $125 that conforms to local building codes and has comparable finishes. I think you can definitely do better than $350, but if you truly believe you can do $125, you are the one who hasn't done your homework. Building in Atlanta and building in Sowal are very different processes. Your builder (please say they have more qualifications than just being published in a regional magazine) will change their tune (and price) quickly when they start pricing rated doors & windows, stainless steel fasteners, hurricane straps, local materials etc.
It would be great if you could achieve it, but I've got $20 that says you can't! Challenge!