Walmart offers the Rubbermaid Mini Ice Pack, model no. FG102610PABLU, for $1. Opt for in-store pickup to dodge the $5.99 shipping charge. That's the lowest price we could find by $14. It's reusable and fits neatly inside or snaps to the bottom of your container.
Oneida offers the Anchor Hocking 8-Piece Glass Kitchen Storage Set for $8.99. Coupon code "FEB15" cuts it to $7.64 and grabs free shipping. (Kmart charges a few cents more with in-store pickup.) That's the lowest total price we could find by $25, although we saw it for slightly less last August. They're constructed of tempered glass and include BPA-free plastic lids.