These are 2 for $25, and large enough to fit an 8-inch duct fan between. https://www.target.com/p/costway-2-in-1-air-purifier-replacement-filter-true-hepa-filte

These are 2 for $25, and large enough to fit an 8-inch duct fan between. https://www.target.com/p/costway-2-in-1-air-purifier-replacement-filter-true-hepa-filter-active-carbon-filter/-/A-87878013#lnk=sametab https://www.target.com/p/costway-2-in-1-air-purifier-replace...