Groupon offers the Purafilter Gold Air Filters 4-Pack in 43 sizes from $19.99. Coupon code "SALE3" cuts the starting price to $16.99. With $3.99 for shipping, that's tied with our mention from a week ago, as much as $39 off list, and the lowest total price we've seen. Each filter purportedly lasts up to 90 days. Deal ends February 24.

Note, the coupon can be used for up to three goods items.