Personally using a room grow I would use the window air unit. Most newer AC's have a great little tool that hardly anyone notices right in the duct that points into the room, there should be a plastic piece in the middle (if your using 12000BTU's or higher) that can be opened or closed - This actually determines where the AC unit gets the air from to condition.

If its pulled out, your pulling air from the outside, conditioning it, and putting it into the room, if its pushed in (comes stock this way) your pulling the air from the room, cycling it, and distributing it, thus sucking out most of the moisture in the room.

There are other options as well, misting fans for cattle have high air flow, and will keep a light mist on the plants, this can of course make them sweat which we don't want, however, if you place the fan correctly and have it set to minimal misting, you should keep your humidity levels up. Check for the plug on the AC first, that might help.

I am using a 12k BTU Haier which ran about $300 I think (somewhere in that range, I know I paid 550 for 2, and one is 10k btus)
The cattle fans can go for as little as $50 and as much as a few thousand - Beyond that point, you can also use a steamer in the room on a timer, this will also help with your humidity levels (I would say a humidifier, but honestly, a vics vaporizer would do just fine on a timer, 20 minutes every few hours or as needed) Those only run about $15