I didn't read every answer that other sent, but we had the same problem.. What my husband did was bought an A/C unit that he installed permanently in the wall.. We had to cut a hole in the outside wall, wire it in permanently, finish and trim out around the unit, and support the unit with bracing.. I was a bit unsure, but it has worked out beautifully.. the area is cool whenever we want it, which is most to the summer.. But doesn't have to be cooled for those times when we aren't using the room. It wasn't expensive (less than $200) and this unit was very energy efficent.. We bought the unit at our local Lowe's or Home Depot, I can't remember which. Made a very uncomfortable room nice to work in anytime we want. Not only is it cool in there, but being a real A/C unit it also takes the humidity out of the room.. a huge plus in the midwest! On top of that he was able to install it high up on the wall (cold air falls down so that worked fine) and it doesn't take up any space at all.. Certainly worth looking into even if you can't do the work yourself. Much less expensive than the idea given by you A/C guy!