HEPA air purifier
i heard you can get an air purifier on the cheap with a box fan, tape, and an air filter. most people seem to be happy with this option over the actual air purifying unit. google hepa air filter box fan to see what options you have.
I did my own like this, then found aLasko fan with a built in filter holder.
I cut off a lot of the back with garden shears to improve airflow and have been happy with it. I use a better filter than the one provided, though.