Walmart continues to offer the 3M Filtrete Allergen Defense HVAC Filter 3-Pack for $15.88. Opt for in-store pickup to dodge the $5.99 shipping fee. That's tied with last month's mention, $11 off list, and the lowest price we could find. Buy Now Features 800 MPR last up to three months select sizes from 14" x 24" x 1" to 20" x 30" x 1"