I put in AC for cheap, as I am cheap.
I have a "people door" that goes from the back porch into the garage. I put this piece of plywood in place and slide the AC into it. I have removed the AC unit by myself, and put it on the shelf I built right net to it. It was at the limit of my strength, and I almost dropped it. So now I get a buddy to help me and it is easy. I can move the wooden frame out of the way, and it is all out of the way. The "frame" is a small door that I can use to go into the back yard if necessary, while the AC is in place.
I have a thread I started on the tech site about garage AC that has the full description of the setup.
My garage is a 3 car oversized garage. The AC mostly cools the work bay where my scissor lift is, and all the tools and workbench. It will keep me comfortable on the hottest days as long as my wife does not go to lunch, and return with a hot car.
It cost be about a buck per hour to run it. So a 8 hour day of working in the garage is 8 bucks of electricity. I can come inside and not be exhausted from sweating. It is 100% worth the cost of electricity. I only run it when I am working out there.