30x40x10 walls and ceiling was $1750 5 years ago , including screws , washers , foil tape for seams and spray can spray foam for gaps in the panels. I used the 1¨ - R-6.7 Its available in up to 3.5¨-R-22. You could use the same thickness as your uprights and stuff it between them and cover with drywall or osb or not. Check your local codes most places require exposed insulation to be covered or just fly under the radar.
