Amazon offers the Sunbeam Comfy Toes Queen/King Heated Foot Warming Mattress Pad for $29.40 with free shipping. That's the lowest price we could find by $5. It features three heat settings and a three hour auto shut-off.

Note: It's also available in Twin/Full for $22.99 with free shipping for Prime members. (Walmart charges the same price via in-store pickup.) That's the lowest price we could find by $9.