Do you consider vertical log buildings such as
to be "alternative construction"?
When it comes to claims of building for $7.50 per square foot......of course its possible. Just not very likely & even less realistic.
But if you're building a place that is up to code on a steadfast foundation, comfortable, has running water, electricity, a legitimate septic system, modern windows/doors, etc......I'd have to think $40/square foot would be a bare bones real world minimum with $50 - $60/sq ft a far more realistic figure.
People always forget.......the shell of the house is just that......the shell. A building that has 4 walls, a completed roof, doors & windows is far from livable.
One will need a water delivery system, a hot water heater, a pressure tank and a network of pipes to route the water through the house. A septic system will be needed. Electricity also is pretty nifty. Then we need a heating system.....and lets not forget a cooling system. Lighting fixtures, toilet fixtures, kitchen cabinets, insulation, interior walls, floor coverings, paint, trim, interior doors, curtains, etc, etc, etc will also be needed.
I saw a show a couple of years ago on Public Television where they showed someone building a straw bale house. All work was completed by a contractor. When all was said & done......the straw bale house cost came in at a not so paltry $100/sq foot!
And, of course, it goes without saying.....trying to sell a straw bale house will not be a quick sale.