Halfords have reasonably priced ones in a variety of sizes, powered from the cigarette lighter socket. Hint: I find refrigerating drinks etc before putting them in a car-powered cooler box works best. If you have a VW/AUDI/Skoda/Seat with A/C, you should already have at least two chiller compartments in the car. These work with the A/C on; handy for water/soft drinks.