Groupon offers the Enviroflow Pollen and Dust Control Air Filter 4-Pack in 44 36 sizes from $16.99. Coupon code "GOOD10" cuts the starting price to $15.29. With $3.99 for shipping, that's $33 off list and the lowest total price we could find, all though we saw them for $2 less last winter. These filters feature electrostatic pleated media and efficiency up to MERV 8. Coupon expires July 3.