With orders of $25 or more, Amazon offers Prime members the Covergirl Lashblast Volume 0.44-oz. Mascara in Black Brown for $3.23. Clip the $3 off coupon on the product page to cut it to 23 cents. Plus, Prime members qualify for free shipping. (Non-members can spend $35 to qualify for free shipping.) That's about $7 less than you could expect to pay at your local store.

Note that this item is part of Amazon's "Add-on program" and can only be purchased with an order of $25 or more.

Update: It's now temporarily out of stock but still available to purchase at this price.