know of any good air filters?

I have a room that's 29" wide, 23" deep and 5 ft high. I have a 250W HPS and a bunch of CFL's.

Since one fan broke I have a 6" whisper fab at 235cfm out of the top and a 6" hole in the side down below for air to come in, and the temp is steady at 84-85 degrees.

I need to replace the top fan with some sort of carbon filter or scrubber, and I don't have a lot of cash. Is there a setup out there that I can buy for less than $70?

not that I know of....thats kinda tight for an odor control budget

What about if I had around $100 to spend? I have two 235CFM whisper fans, I need something that isn't going to restrict air flow and burn the fan out.

How easy does air pass through the carbon scrubbers?