Kmart offers the Zak Designs Disney Frozen Elsa, Anna & Olaf Placemat for $2.69. Opt for in-store pickup to dodge the $4.99 shipping charge. That's the lowest price we could find by a buck. It measures 17.75" x 8".
A close price: Kohl's offers it for $3.39 with in-store pickup via coupon code "DEALS15".