Humidifiers and purifiers are two seperate beasts. If you are talking about portable, just go to Sam's or Costco and get a cheap HEPA filter, and a humidifier.
Know that portable humidifiers must be cleaned once every 5-7 days, and refilled at least once a day. That gets old. However some people get along fine in the Winter by just using the humidifier in their bedroom at night.
If you are in a house, it's better to have the humidifier installed into the forced air system--no cleaning or re-filling.
EDIT: last I remember, you could get HEPA for large room for ~$120 if you shop around. They all work about the same.
EDIT2:
Sam's 2 for 1 + remote $139 This includes a built-in ionizer, which can be switched off if desired.
A cheaper smaller one.
I didn't bother looking anywhere else... You can spend more, but you won't get much more for the money.