1) A few years ago, a gentleman working abroad in China posted his air purifying workaround here on HN (original article: https://scienceblog.com/73679/grad-student-rigs-cheap-alternative-rival-1000-air-purifiers-smog-choked-china/ ). It motivated me to "build" my own version. After many experiments with brackets, hardware, and duct tape i cobbled together a design that cost about $60. Then my Dad came along and cut the price down to $30 by just putting the filter on the back, letting the suction do the work of attaching the filter (the original design i ripped off used a barrel fan + HEPA filter; mine is a box fan + furnace filter).

The thing is amazing. Placed next to kitty litter box it eliminates the smell almost completely. It pulls hair and particulate matter out of the air effectively, helping keep work and leaving spaces fresh. The original Ideageneer tested his to compare it to the very expensive consumer models available and his was on par with their's at a fraction of the cost. I have not tested mine, but using his methods it would be simple to do so. While there is the cost of electricity for running them, as well as the occasional fan replacement and the more often filter replacement, the cost comparison with an expensive Phillips Unit is astounding.