Walmart offers two Stanley FatMax 140-watt Power Inverters bundled with two Freestanding Keychain LED Lights for $29.98. Opt for in-store pickup to dodge the $4.97 shipping charge. That's the lowest total price we could find by $20. (For further comparison, we saw a single pack for just $5 less last week.) The power inverter plugs into a car cigarette lighter and features a 1-amp USB port and two outlets.