PricePlunge offers the Duracell 30-watt DC to AC Mobile Power Inverter with USB, model no. DRINVM30, for $8.49. Coupon code "coldplunge5" cuts it to $8.07. With $4.98 for shipping, that's the lowest total price we could find by $5. It converts 12-volt DC battery power from a vehicle into 120-volt household AC electricity.