I offer a fully built fan system for $35 on the FISD and Legion boards...
Very quiet, good continuous battery life (4hrs), can use a USB rechargable battery pack (USB cable is included), and shipped price is under what other vendors offer. I've sold 28 systems and have gotten a lot of kudos from fellow troopers who simply love this system.
http://forum.whitearmor.net/index.php?showtopic=3513
http://www.501stforums.com/forum/viewtopic.php?t=17238
Doing it yourself, the cost of fans, wires, switch, solder, and battery pack from RadioShack comes very close to my asking price.
Kev
TK-1422