The Ionic Pro

The Ionic Pro is a lot like The Sharper Image's Ionic Breeze, but it's a lot cheaper than the original ever was. It offers the same lack of maintenance as well. Just pull out the magnetized filter bar, clean it off, then replace. There's nothing more to it than that. As there's no fan, it's uses a lot less energy and is quite a bit less noisy than HEPA air purifiers, though generally less effective. However, if a cheap solution for cleaning the air in a 500 feet is what you're looking for, but you don't want anything that makes noise, then an ionic air purifier might still be your best choice.