HD has 12 packs of air filters on sale 5/27/14 Deal of the Day

 http://www.homedepot.com/SpecialBuy/SpecialBuyOfTheDay?storeId=10051&langId=-1&catalogId=10053&cm_sp=MD-_-BODY-_-SBOTD.U4Su_igQF5Y

The prices are pretty good for a case of 12 you can get year or more of use out of all of those filters. The only problem is if they have your size in stock. It’s one of those things everyone uses even though its not tool related.