So some negatives of the range hood are that they are loud, large, heavy, routing the venting would be ugly sticking out the top, probably way to many CFM, and are very hard to seal completely (lots of gaps between bent sheet metal etc. I'm rethinking my approach.
I found out how to calculate the CFM of the fan needed to pump out the air.
If the enclosure is 2.5 x 2.5 x 2.5 feet and I want fresh air in the case every minute I only need a 16 CFM fan. A cheap 120mm PC fan can easily do 40-70CFM.
I found a PC fan with a variable speed controller built in for $20. Look at that knob on the speed controller! :D
http://www.amazon.com/SilverStone-FM...+speed+control
This would allow me to vary the speed without having to engineer something and would cover me in case a fixed speed fan was too fast or slow. This fan should be much quieter too!