I shudder at heating costs with 14 foot ceilings. I'm willing to replace the
existing room walls if that is needed. That room needs more outlets anyway.

I envy you the size available.

Have you considered walling off & ceiling a smaller area for A/C
purposes and using the area above for storage? Say, 9 feet high by
400 - 600 sq ft for the working shop and part of it or a separate small
room for a spray booth. Separate small room for air compressor, chip
collector, and dust collector. For insulation you might look into foam
panels. Easy to put up, but I don't know how effective.

I'm just down the street from you and today I broke down and ran the
shop A/C the whole time I was there. Third time this year.

It's only money.
-J