With orders of $25 or more, Amazon offers Prime members the M&M's Crispy Chocolate Candy 1.35-Oz. Bag 24-Pack for $9.75 with free shipping. (Non-members can spend $35 to qualify for free shipping.) That's $5 under what you'd expect to pay for this quantity of M&M's at local stores.
Note that this item is part of Amazon's "Add-on program" and can only be purchased with an order of $25 or more.