But furnace filters are a lot cheapee than most replacement air purifier filters, and that's before you buy your furnace filters at Costco or surplus.

But repairable, cheaper to operate (power and consumables), and quieter for the CADR than Coway.

https://housefresh.com/coway-airmega-250s-review/

https://housefresh.com/nukit-tempest-review/