At Target, buy two select Filtrete filters and get a $5 Target Gift Card for free. Plus, subscribe to cut an additional 5% off and bag free shipping. Deal ends March 6. A couple of best bets, with prices after discount and comparisons assuming you'll use the gift card:

• 2 Filtrete Allergen Defense 12x25" Filters w/ $5 Target GC for $7.11 (pictured, $23 off)
• 2 Filtrete Allergen Defense 10x12" Filters w/ $5 Target GC for $11.86 ($18 off)