Insulate, insulate, insulate!
What good is a garage/shop if it's too hot to function in?
That door is radiating heat into your shop all day, as is the ceiling. The rigid foam insulation in 4X8 sheets is easy to cut to fit and goes up quick.
Insulate the ceiling/door first, then the walls as $$$ permit. Do the walls facing the sun first. If the roll insulation is cheaper (probably), use it on the walls.
To make the airco effective you must insulate everything: the door, walls and ceiling. Otherwise your air unit will be fighting a losing battle and you'll just be wasting money.
Get a ceiling/attic fan to draw out the heated air. Just moving the air will make the room easier to survive in. Put an inlet vent on the coolest wall. Add the airco unit (wall mounted) as $$$$ permit. Only run it when you're in the shop to keep the cost down. The insulation and moving air should keep the heat well below what it is at now.
Sure it costs a few bucks, but it's well worth it and you don't have to do it all at once. I did mine a little at a time and it made a tremendous difference.
BTW, if you can plant some shade trees to block some of that intense sun, go for it.