you can get brand new oreck's on ebay for $175, i don't know why they are so expensive on the home site.
i am always suspicious of the hepa filters because the allergens or dust mites etc just stay int he filter and could recontaminate your air. i like the filters that have the removable electrostatic plate that you can rnse in the sink and replace. that way whatever you take out of the air you can eliminate altogether.
which specific model did you get from ozoneman? does it just generate ozone and ions, or does it also remove dust and particulate matter?