Yeah they are expensive but the best I have found. The 45i is for like 700 square feet for $400. The nice part about Alen purifiers is the filters last just about a year and lifetime warranty

I went down a rabbit hole when California nearly burned down in 2020 and after lots of research came to the conclusion that buying 7x $100 hepa filters is better than buying 1x $700 filter. So an inexpensive Winix ended up being the best for me. One for each room. More air cycles and much less noise when they're scattered throughout the house. This is just for particulate matter. If one cares about volatile organic compounds, VOC's, they need to invest is several pounds heavy charcoal filters. The thin ones that come on most filters don't do anything other than act as a pre-filter to catch the large particles.