Hi there
Have you thought about using magnets to put on the cars at all instead of going to the expense of painting cars? These magnets could be as big as an A4 page with the business name printed on the magnet. I had two made up for my business and put them on the driver's side and passenger side of my car, and I am in the process of ordering some more because they worked so well. If you have the time to contact a fridge magnet company, they could possibly send some prices and the magnets themselves are not all that expensive to have made up. Hope this helps.