Hi,
I have also considered the Sharper Image purifier, especially the one with UV light, however in a health book I own by D. Nina Silver, who specializes in Rife frequencies and other alternative health therapies, she recommends something called the Aranizer, and says it is the best thing you can do to purify your air. I did a search on it and it is more expensive than Sharper Image, but if the results are so god then I would think it's worth it. I still can not afford it though.
Let us know what you decide.