Here are a couple of different models from Kathy Ireland to consider: http://www.lampsplus.com/kathy-ireland-home-air-purifiers/
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I have a RabbitAir BioGS SPA-421A
Its $330, which is slightly above your price range, but its well worth it. I have bad allergies which lead to bad asthma and this thing has been a true godsend.
Its quiet in all but its quietest modes and has electronic sensors to crank up the filtration when air quality decreases. Also, guests can never figure out what it does. It looks futuristic and not like medical equipment.
I would totally buy it again. In fact, I haul it to my mom's house when I come home to visit. Its that great.