first question is how is your light vented,or do you have a cheapo batwing.you need to pull the heat off the light first.If your light isnt enclosed and not pulling heat off your dumping raw heat into your grow room.in the case of a batwing, a fan at the top would relieve some of the heat but your still gonna have issues.ideally a fan pulling heat off the light and one pushing cooler air into the room.As for being on a budget,Ive found i spent more money on cheap fix its than just saving for the right equipment.in the long run it is cheaper for the more expensive equipment.I bought a 440 cfm fan for 90 dollars.I have also bought a 10" inline fan (not sure of the cfm) for 40 dollars.both work great.The little fans ive bought from lowes or home depot or wally world are all burnt up