When calculating inflation, economists look at the cost of products in thousands of locations across the United States. In Lexington, though, the easiest way to see how prices are going might be to look at the famous Burger Shake sign on East New Circle Road. As prices of everything from corn to clothing have soared this summer, the iconic local fast-food sign saw a change, too: The cost of a burger went from 84 cents to 99 cents this summer. "All of our costs started going up like crazy," co-founder Joe Isaac said. "We couldn't hold the line anymore.