Walmart offers the Iris 6-Quart Modular Storage Box 10-Piece Set, model no. 585010, for $26.09. Opt for in-store pickup to avoid the $4.97 shipping fee. That's the lowest price we could find by $6, excluding the mention below. These boxes can stack and feature a snapping lid.

A close price: Sears has it for $27.22 with in-store pickup.