Today only, until 9 am ET (or 100% claimed), Amazon offers Prime members the M&M's Halloween Peanut Chocolate Candy 12.6-oz. Bag 6-Pack for $13.03 with free shipping. (Non-members can spend $35 or more to get free shipping; otherwise shipping adds $8.59.) That's $9 under the lowest total price we could find for this quantity of Halloween M&M's elsewhere.
My M&M's offers the M&M's Pre-Filled Halloween Party Favor 50-Pack for $50 plus $9.99 for shipping. That's $1.20 per pack, $40 off, and the lowest total price we could find. Each pack is filled with a custom Halloween-blend of M&M's. Deal ends October 31.