I'm looking to buy an air purifier. Suggestions?!

I'm looking to buy an air purifier. Suggestions?

My boyfriend has bad allergies and terrible asthama. My roommate has a dog and cat so I think it's mostly pet dander that ends up bothering him in my room, even though i keep the door closed all day. Does anyone know of a good air purifier that is relatively cheap but good for asthama? I know i have to find one with HEPA, but I'm wanting to spend maximum 150. Thanks all!

i have asthma and im allergic to pet dander and i have a long haired and a short haired cat and i'm fine. Does he have an inhaler and or nebulizer system? I would try that first. Whenever he has an asthma attack, give him an albuterol. And if you have one, give him a pulmicort twice a day. Sorry this was off topic. PS Try a Homedics home care store.