Walmart offers the Wenzel Emergency Blanket, model no. 50330, for $2.27. Choose in-store pickup to dodge the $4.97 shipping fee. That's the lowest price we could find by $4. This waterproof aluminum-laminated polyethylene blanket also reflects heat and wind, and measures 84x52".
Of note, Amazon offers it for the same price when you purchase it as an add-on item with orders of $25 or more.