That sounds like how I built the fence. Do you think I would be approved a permit to build with 6' girts?
In theory, I could find a relatively cheap box truck, but I would probably need to drive it up from the valley, use it to haul stuff to the dump, undo the U-bolts, set up the box in the back yard, and sell the truck.
That sounds like a weird solution!
I have been trying to price structural insulated panels, but while I find many sites for various manufacturers, I find very few places actually selling them.
This site says a 4.5-inch thick panel is R-16 and costs $162.56.
I would need eleven panels: $1,788.16. We are approaching aircrete territory, but I see fewer ways to mess up, and no theoretical catastrophic failures.
This place has 1.5-inch boards, 2", and 6.5-inch boards, but only have OSB on one side, although I could hang drywall on the inside. R-22.1, $123.95 each, and $1,363.45 for 11.
SIPs are supposed to be stronger than normal wooden frames, but Ray-core builds SIPs with normal wooden frames and claims that they are as little as half the cost of their competitors--but they do not advertise prices:
https://raycore.com/sips-panels-cost-pricing/
They say a 3.5-inch wall is R-26.