It does seem to be a mostly turnkey price, including a (I'm guessing) slab foundation and running sewer, water, and electrical, and placing the structure, so th

It does seem to be a mostly turnkey price, including a (I'm guessing) slab foundation and running sewer, water, and electrical, and placing the structure, so that price is a lot less crazy. The other thing they have working against them is cost per sq ft goes up with smaller builds since you still need expensive spaces kitchen and bathroom and they can only shrink so far. In most high cost of living places where building ADUs makes the most financial sense I'd be surprised if you could do something like this start to finish for much less than 400k between permits, variances, drawings, groundwork, utilities, construction and finishes. The foundation and utils alone could be 100k+.