This is what I bought from Amazon:
HEPA Air Purifier
Its a HEPA certified air purifier that I keep near my ratties cages and running pretty much 24/7. My room is about 15'x15' and when I have it running, I really can't smell them all too much, if at all for about a week. When I take it from my room, I can definitely notice a huge difference in how much it smells in there before a cleaning.
The air filter should be cleaned maybe once a month, and that only takes a couple of minutes with a wet rag or a HEPA vacuum.
I have pretty bad seasonal allergies/asthma and at one point they were doing major construction right outside my apartment that kicked up a lot of dust, so I was able to justify the $90 price tag pretty easily.