Jeremy, My CPAP machine, AirSense 10, has a small air filter built in. It isn't HEPA but it helps reduce some garbage before it gets to the machine. I did notice that the filter on my last machine wasn't as dirty after I started using the Honeywell air filter.
The reason why the prices have increased is supply and demand, with COVID more air filters are selling, prices go up. It is winter in the Northern Hemisphere as well, and when people are stuck in doors people worry more about air quality.
tallullahjo (I don't know if you have returned to the forums)
An article about different air purifiers. I don't trust most "best of" articles on any item, there are many and each article produces different results. If there was any science behind the article there would be one or two devices across all articles that stand above the others. However, knowledge is power, getting as much information as possible is helpful.
https://www.thegoodtrade.com/features/best-home-air-purifier