Martin (Finn) had a really cool site that he sent me the other day with some really cool fans that would be right up your alley. I can't remember the link though Hopefully he'll chime in soon
dude this is a piece of cake! head on up to home depot and pick up some 50-100 cfm bathroom exhaust fans for $10-$30 depending on cfm and style. they work great and you can run air duct to expell the heat outside...
I got mine at wall mart they are clip ons I clipped them onto the ball valve handle and they are behind my tank which has the canopy open at the back and the fans are slightly larger but work great are quiet and were cheap
Paul
keep in mind the more cfm the louder the fan will be as well. the bathroom vents are a bit louder then other fans but they move 5 times the air and work much better...
A while ago, I was in search of the highest cfm per decibel fan I could find. I ended up buying some there. I got 12vDC as opposed to 120vAC, so I powered them with a "wall wart" power supply from KMart, though thrift stores are GREAT places to find these "wall warts."
One thing you'll want to keep in mind is that the smaller the fan, the louder it will be for the same cfm. Stated simply, a larger fan can move more air. Additionally, the larger fans have a lower pitched whine, which is easier on the ears.
If I recall correctly, the fans I picked up were about 115cfm @ 34db. They were about $10/fan.