Preparing the ground isn't mentioned. If you've never tried to make a chunk of ground perfectly level and compacted so that your shed won't sink and tilt... you won't get it right by yourself. Not the first time, anyway.
"After the units are built in the factory, they are fork lifted into a truck and driven to your property address. Once the truck arrives, a forklift will take the unit out of the truck and place it in place on your property."
This does not sound to me like they are doing anything beyond just building and finishing a box, and the price is fairly absurd for that.
That's if you are looking for some premium glass that won't shutter into a thousand pieces and hurt you. Same for steel, aluminum, high quality wood, etc...
So yes, it can be very expensive. A cheap wooden dwelling can be pretty cheap though.
Couldn't just make that $0 with a $9k purchase?
$9k seem expensive, but I don't know the price of these things so half willing to accept it. Then seeing they are charging $31 for a power cord now makes know they are charging too much for the the main thing they are selling.
And as a bonus, they'd know your local codes and inspection requirements.
I used to know someone whose entire house (about 900 sq ft in Beltrami county, MN) cost less than that!