HK, you are going to think I am crazy here, but, here is an idea.
Build a room inside your garage, either with permanent walls, or "walls on wheels",,,,,,make them tall enough to seal off at the top,,,,,,then put in a door if you need to,,,,,,,and put a window mount AC unit in one wall, between your work area and the rest of the garage (since it is already unbearable in the main garage, a little more heat won't hurt anything)
it wouldn't have to be a large room,,,,,,an area in one corner about the size of a bathroom would do it, and the smaller the room, the cheaper it would be to build, and the easier it would be to keep cool
I was building something that same size on the open back porch when we decided that I could just switch to acrylics and work inside the house,,,,,,,,,,,,but, the "room" I was building would be about the size of a pickup bed, just enough room for a bench, a compressor, the chair and clearance for the AC unit
I was doing it to fight the humidity we were having a problem with, here in Tenn, and I might finish it up one day, just to have an alternate workspace
Rex