i am sure you could find all of the needed ingredients for a lack of a better word, to build your own diy carbon filter.. like i know that petsmart sells loose activated carbon for not too much..
i am sure there are probably a million do it yourself carbon filter tutorials on the net, just do a google search for it and im sure a ton will pop up for you and get you going in the right direction..
a good carbon filter can run about one hundred for a smaller four inch one, up to a couple hunred or so for a big ole one...
you should also check out roseman diy odor control bucket.. it is just like the one in the newest edition of hightimes.. he takes a bucket, and drills a lot of holes all the way around the bucket, adds a few inches of water, and some ONA, and then puts a fan on top of the bucket so that the fan pullsin all of the stinky grow room air, forces it through the water/ONA mix, and out through the holes drilled in the bucket.. my description really does it no justice.. you have to see it for yourself, and roseman says it works killer, so i would say it probably works killer, lol..
hope this helps you out some