Here's another cheap one to look for. I've seen it as low as $99 (out of stock) but $150 in a few spots down from $749
MasterCool 2,300-sq ft Direct Whole House Evaporative Cooler (7000 CFM)
Item #: 226325 | Model #: ADA71
http://www.lowes.com/pd_226325-12934-ADA71___?Ntt=22632