Insulation doesn't cost, it pays! Urethane spray foam on my two HydroSwing doors, (and for sure, over the frame not just inside the frame, to preclude thermal wicking) AND on my hangar's concrete walls ( it's dug into a hill side, and instead of framing the last 2' of wall height it was simpler to just make it them all concrete), and THEN I framed out 2x4 interior walls with batts. Cool in the summer, never below mid 40's in the winter, even if no heat and single digits outside. OSB over the studs, it's nice to be able to staple/screw things to, unlike concrete or steel walls, more homey.
I have a pilot friend whose father started their spray foam biz over 40 years ago. Spraying the big potato cellars around here takes a lot of foam! I got a bit of deal as a result, but still expensive, but I didn't care as it is the best way to go. I sprayed white latex paint over my doors, I guess I could claim it's fire rated but it ain't and I don't care. It really brightened the hangar up. Since I knew I was going to live in the hangar for about a year before building the house, it was an easy justification to insulate as well as possible, same with my shop having a full bathroom with laundry facilities: pretty fancy for a shop but worth it as my other alternative was laundromats and not showering for a year!
He told me once that according to his father, the foam was invented by the Germans during WW2, as a method to raise sunken submarines. It worked, but was too impractical, as the cleanup was a bear, it's insulating properties only being discovered later. Good story if true.