I own the HAP422 and it has been the greatest thing since air. I have allergies to most cedars and cats. This has made a noticeable difference since day one. It has been well worth the money. HEPA filters are the real deal.I also have been looking for the filter and haven't been able to find one. I checked amazon to see what they were asking, and I'm flabbergasted at the high prices.Folks, go to the Holmes website. The filters are $13 there. I'm going to order 2 now.