The break even in a big show is no different to the break even in a small show. At a small show, you need to cater for a smaller group of people, thus sell less merch. At a bigger show, it is no difference, only more money comes out of it, which pays the higher costs of putting together such a show. Your earnings only go up slowly, pretty much just enough to get yout through. It all makes sense that they charge like they do, trust me!