Walmart offers the Rubbermaid Lunch Blox Sandwich Set, model no. 1806231, for $7.92. (Amazon charges the same.) Opt for Site-to-Store pickup to avoid the $4.97 shipping fee. That's the lowest price we could find by $10. Designed to save spaces in lunch bags, these reusable containers are BPA free and dishwasher-, microwave-, and freezer-safe.
A close price: Kmart has it for pennies more with in-store pickup.