Home Depot offers the Filtrete Ultra Clean Bedroom Replacement Filter, model no. FAPF02-4, for $16.23. (Walmart charges the same.) Opt for in-store pickup to dodge the $5.99 shipping fee. That's the lowest price we could find by $2. It is compatible with Filtrete models FAP01-RS and FAP02-RS, and it purports to capture 99.9% of large airborne particles and allergens.