Are there good quiet air purifiers that I can buy?

As a consumer of course you are looking for an air cleaner that costs $1, can clean the volume of air in a stadium in a minute, and is as quite as a hummingbird.
Back on planet reality you get what you pay for. Cheap air cleaners have filters that don’t last long and loud motors. Electronic air cleaners need regular washing. That’s ok if you can remember to do it and have the time! They are also susceptible to generating ozone, but ozone can be eliminated with proper maintenance and a carbon post filter.
A good place to start is the Consumer Reports article on air cleaners. Keep in mind not all air cleaners got rated.
Personal story – Friend of mine has allergies, purchased our PM-400 HEPA air cleaner and loves it. The PM-400 has one of the largest HEPA filters and a 13-pound carbon filter for collecting odors. They put it in the hallway between their bedroom and the baby’s room (diaper odors). When they are gone they crank it up and when they get home they turn it to a low quiet speed.
Check out our air cleaners at http://www.air-quality-eng.com

Oreck is expensive but worth it. I also suffer from allergies, and my two machines are wonderful.