im a comp nerd soooo get a computer fan, they range in all sizes, id recommend a 8cm *80mm* or 12cm *120mm* fan. hooks up to 12v current and can be had for a couple bucks at most.
id get 2 80mm fans so u can slit the different with them. they actually work a lot better than i thought. my amp used to get burning hot, with 2 80mm fans a few inches away from the amp blowing directly on top, it barely gets warm and doesnt blow anymore fuses
http://www.directron.com 10 dollar limit :-\
http://www.newegg.com
http://www.buyxg.com