The best/cheapest way to do the filter thing is to buy a big box fan, one of those big square ones, and then tape a HEPA central air filter to the intake side. It will cost 1/10th of what a regular room filter costs, but it will be quieter and cost less for replacement filters. You can get really high quality filters at most department stores. I usually got my filters at lowes or home depot, the best superduper anti-allergen 3M filters I could find.