I've bought two of them for work.
I selected a nice used 40' a few years ago for $3500 delivered about 60 miles. My guys built stud walls and ceiling joists, added fiberglass insulation. We ran conduit in the walls, cut a hole in the side for a window unit, put T-111 on the ceiling and walls, built work benches, and painted the floor. It has been perfect for 5-years.
I just bought a new 20' for $4400 delivered about 80 miles a few months ago. It was made in China but seems well made. We added metal stud walls and ceiling joists, styrofoam blown in, 5/8" CDX walls & ceiling, with painted corrugated galvalume? screwed over the CDX, with external wiring in conduit. I had a contractor cut two doors and two window units in it. It is to be used as an analyzer building. I believe we will be able to insulate it with a couple of ice cubes, that foam is fine.
For my personal use, I would buy a good use one, build stud inside walls, blow styrofoam in, and cover with T-111. I would have one if my neighborhood restriction would allow it but they don't.
But maybe it's just me...