One option is to pick up a car battery and hook it up to an AC inverter. Charge it overnite with a 2 amp charger and it'll run all day. Total cost excluding the battery is under $40 bucks.

A 12V in, laptop power out gizmo costs 20 bucks or so on amazon. They come with a standard automotive aux plug which is common in the power banks so should be wide input range and take 10 -> 14 volts.