Car show question......

I didn't read all the responses. But, I'd say don't invite ANY car group. Open it up to the public by flyers. I bet you'd have some "weenies on wheels" food stand ask if they could sell there, then your food/pop is taken care of.
Have the store buy three 5.00 dollar tropheys for 1st, 2nd, third by "people's choice" voting. Anyone (everyone) gets a piece of paper and they can choose their top 3. A local town does it that way. The "club" snobs can come.... with their tail between their legs :D