This obviously isn't my garage, but it's what we did...
And this is what we used...
http://www.homedepot.com/p/Rmax-Thermasheath-2-in-x-4-ft-x-8-ft-R-13-1-Polyisocyanurate-Rigid-Foam-Insulation-Board-613010/100573703
If you cut your pieces tight, you probably don't even need glue as they will slide behind the edge of the panel where it attaches to the next panel.
Use this in your walls,
http://www.homedepot.com/p/Owens-Corning-R-13-Kraft-Faced-Insulation-Roll-15-in-x-32-ft-RF10/202585857
Then buy your 4x8 sheets of white or brown pegboard, and finish off your wall(s)
With this set up, we can turn the A/C on in our shop in the morning, and within an hour have the temp down 15-20 degrees and it'll stay that way if you don't open the big door, only turning on a handful of times for a short period. Granted, we have a 2 ton package unit, but it's also bigger then your garage.
Pick out something from this list,
http://www.homedepot.com/b/Heating-Venting-Cooling-Air-Conditioners-Coolers-Air-Conditioners-Portable-Air-Conditioners/N-5yc1vZc4m4
Park it next to you and you should be good.
We used this on the outside where our vent tube ran into the wall. Painted it the color of the house and it looked nice.
http://www.homedepot.com/p/Master-Flow-4-in-Round-Wall-Vent-Black-WVA4BL/100396976
Here's a vent tube that would work.
http://www.homedepot.com/p/Whirlpool-6-ft-Dryer-SecureConnect-Vent-4396010RP/202204725