With orders of $25 or more, Amazon offers Prime members the Sunbeam Heating Pad with UltraHeat Technology, model no. 756-500, for $5.23 with free shipping. (Non-members can spend $35 or more to qualify for free shipping.) That's the lowest price we could find by $9. It features a slide controller with large switch and machine washable cover.
Note that this item is sold as part of Amazon's "Add-on program" and can only be purchased with an order of $25 or more.