About 6 years ago, I got a Hunter 30065 w/ Ionizer that changed my life. I thought for sure that having a running nose, not sleeping well and sneezing all the time was just a part of my life, but all of that stopped when I got that air purifier. When I started dating my girlfriend, I couldn't be at her place for more than about an hour before I was coughing and having trouble catching my breath (she has a dog). We got a Holmes air purifier for her bedroom. Took it home, turned it on and went out to dinner. By the time we got back, I had no problem breathing there at all. Now that I live there, we have both of them going full time.
Both of those are ones that have filters that you have to replace, so I can't speak to the cleanable ones, but you can find filters of a much lower price on Amazon. Thats where I get all of mine.
http://www.allergybegone.com/hunhep65airc.html
http://www.target.com/p/Holmes-HEPA-Type-Allergen-Air-Purifier-Black/-/A-13870675