I've gotten several quotes to do my sidewalls which total ~2400 sq. ft. Lowest bid was $6,800 and highest bid was $7,800 for 3" thick closed cell. Middle of the road that's $1/sq. ft. per inch.
Concrete for my 2400 sq. ft. pole building poured @ 5" thick with a 20' trench was ~$7,500 and they did the dirt prep work. I installed the plastic vapor barrier, 2" foam, and pex tubing after the prep work and prior to the pour.
Curious on your heating bill costs. Thinking about building a similar sized shed and wondering if I want to try keeping it heated all the time or whether I should go with a weekend warrior approach.