I have read somewhere that splashing water creates negative ions which neutralizes the odors in the air. Not sure if it is cheap to make. What I suggest is getting a flat tub, a bottle of the odor eater strays(the ones where you can spray into a stinkin garbage can and it will smell good), and an old style of the aquarium filter that works like a waterfall. Mix the odor eater with water and mount the filter (I suggest don't use any of the water filtering material though) so that it can create as big a waterfall as posible over the tub. Find some sort of lid that fits over the tub but let enough room for the water to return to the tub, mylar the tub and lid of course. With circulation the system should work, although it might create Humidity problems.
There is another method I've read that sounds promising that is getting a cheap ionizer and attach it to the plants. It ionizes the plants and eliminates the odors although the author warned that the static buildup will give a slight shock to whatever that touches the plant. Anyways, good luck with your battle.
