Amazon offers its Prime members the Bob's Red Mill Gluten-Free 21-oz. Brownie Mix 4-Pack for $11.96. Checkout via Subscribe & Save to cut that to $11.36 and bag free shipping. That's the lowest total price we could find by $6. It's vegan and Kosher Pareve.
Be sure to cancel your subscription once your order ships to avoid being billed for further shipments.