How much is a full slab of ribs

Belzoni, MississippiLately i have become a fan of grilling. Been working on my own technique and i have gotten pretty good at it. I dont mean to brag but my ribs could hang with some of the best. But anyways, my wife and i run a small theater where we have talent shows and musical concerts. I want to grill and sell some rib plates. Im wondering how to go about pricing them to sell and make a profit. A slab of ribs here will run me about $12 - $15 bucks. So So how do i market them and sell them to where a make a couple of dollars? How do people sell ribs?