Amazon offers the Hygloss Corrugated Bright Sheets 8-Pack in Assorted Colors for $4.56 with free shipping for Prime members. (Walmart charges the same via pickup.) That's the lowest price we could find by $3. It includes eight sheets of 8.5" x 11" corrugated crafting paper.

Update: The price has increased at Amazon; however, Walmart offers it for $4.39 with in-store pickup.