Target offers the Biddleford Heated Full Mattress Pad for $24.98. Pad your order to over $25 to bag free shipping; otherwise, shipping adds $7.20. That's the lowest total price we could find by $17. It's made from polyester and features automatic shutoff and lighted control.
Of note, Target also offers it in Queen for $34.98 and King for $39.98, both with free shipping. They're price lows by at least $25.