Depending on how big your room is you don't need to buy one...
I use them and they are very efficent, they chill your room and create air circulation. They work well for both grow rooms and bed rooms... Trust me i use them and i live in south Texas so its hot as hell sometimes.
here is a basic guide on how to build a small one (in an airtight room small is o.k.)
Very basic:
Materials: 2 five gallon buckets
2 yards of burlap (apx 2 yds. by 2 feet)
1 fan (apx. 24" by 24")
2 supports or something to hold the buckets
Instructions:
Get fan and aim toward area you want cooled. get supports, anything that will gold buckets 1' foot off the ground. Put buckets on supports and fill 3/4, or more, full of water, cold water helps and ICE helps even more. Get your burlap and put one end in one bucket so a good amount is in water, then put other end in the other bucket of water so the middle drapes in front of the fan. Now just wait bout 7 minutes to let the water soak down to the middle then turn on fan.
There you go a swamp chiller!
NOTE: Do not get any of the fans electrical components wet. (don't drape burlap behind or on fan)
OH YEAH and also remember to replace the water periodically.
If you need any more help just ask and i'll respond.