I’m in the middle of trying to figure this out with a friend by building an off-grid tiny house and this is pretty accurate. With our labor at a nominal rate (30/hr) it’s coming out to about $250 per square foot. We think on the next one we might be able to get down to $200 maybe $175.

Interior is not done yet, but exterior is: https://imgur.com/gallery/KbPlbPR

That 250 psf includes everything you need to live from the get go except you have to fill the 50-gallon water tank.