if your looking to get a small fan to hang to blow on your canopy id suggest going to like walmart or kmart and getting alittle fan like this :
http://www.walmart.com/ip/Barjan-1126-6-inch-Clip-On-Fan/26381001 for like $12. i hang mine down by zip ties, that way i can raise it as i raise my lights. if moneys not a problem id suggest getting two of those fans blowing in opposite directions, lots of air flow.
my ballast is dimmable too. costs a little more but for a one time buy, id rather spend more for something thats gonna last longer and do a better job, you know what im talking bout.
right now i got 5 going. id like to do 6 but one of them didnt make it
i can only fit 4 in my tent because the pots i use are too big (glass 1/2 full view- better root system) and i still have my ol rubbermaid setup that i grow 2 smaller plants in. i just recently heard and plan to buy these:
http://www.roguehydro.com/hydro-supplies-superoots-air-pot-3-gallon-equivalent/ they are smaller (which will hopefully allow me to fit 6 plants in my tent plus the two in my rubbermaid) but still equivalent to the 3 gallon pot size, which is the perfect size pots for our tents seeing as how we can grow a 3 ft plant easily. its a one time buy of like $60 but it will allow me to grow two extra plants...
every grow after.