yeah you can build a carbon filter that you would buy at a grow shop, for cheap.. prob less than 25 bucks... i'm going to be making one this weekend, maybe i'll post a thread w/ steps..
search the web though, there are a bunch of great sites that give you idea's on how to build one..
but from what i have read, to stop the most odor molecules from leaving your grow area, is activated carbon..
all your really trying to do is build something that can hold the activated carbon ( which can be bought at any pet store that sells fish products ), and pull air from grow room through...
very simple idea...
anyways , search the net..