I hate to be the guy that just posts YouTube videos on Mooneyspace but I found another one that might be of interest to the group. Using a 5 gallon bucket, some styrofoam, and a small fan this videos creates a device that should cool our airplanes in the summer. They hook it up to a solar panel in the video but I'm sure it wouldn't be hard at all to hook it up to a cigarette lighter. Should save you $350+ over the commercially available ones.
http://www.youtube.com/watch?v=HxSLbpAwibg