With orders of $25 or more, Amazon offers Prime members the Rubbermaid TakeAlongs Twist and Seal 2-Cup Food Storage Container 3-Pack, model no. FG7J0000TCHIL, for $2.26 with free shipping. (Non-members can spend $49 to bag free shipping.) That's the lowest total price we could find by $5. They're microwave- and freezer-safe.

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