I'm using a detached 2-car 20ftX20ft garage with no windows to do a boxing workout and it get's hot and steamy quickly if there is more than one or two people in there at the same time. The floor gets dangerously slippery also. I got a dehumdifyer and it works but it actually adds more heat to the garage which will get unacceptable in a couple months, plus it costs almost as much as the portable A/C from Coscto above. I can return the dehumidifyer to Sears in the next week minus a restocking fee, so I'm thinking ordering the portable a/c linked above.
I'm sure the 10,000 BTUs is probably not enough to really cool the garage to a comfortable 76 degrees on a 100 degree day (though it says it could work for up to 400 sq ft), but if it can at least drop 10 or 15 degrees, bring in fresh outside air and exhaust the hot, humid air it may be worth it.
Since there are no windows, what would be involved in cutting holes through the drywall to mount the intake and exhaust tubes? It is a newer house with stucko on the outside of the wall. I think I would rather have two small round holes for the tubes to go through rather than a large hole that fits the provided rectangular window adapter. I do not want to cut through studs in the wall and make a giant opening for a standard sized window a/c, so that's the main reason I want the portable unit.