What is the best air purifier for dust?

I moved to NYC and hate the dust. I'm an asthmatic and allergic to dust. My room is 12 x 15. Have tried Hamilton (hepa), researched on ozone purifiers (everybody, almost, says it's bad), tried ionizers (did not work). What else is out there, AS PER OTHER"S EXPERIENCE, that won't kill me with the price tag and replacement of whatever (e.g. filters). If somebody answers for me to move, it's not an alternative as of this time. Please just help!!