Bluegrass music at Cumberland Caverns makes another sound when you take away the banjo. It goes cha-ching.Three days of live performances for the PBS program Bluegrass Underground left some memorable moments from stars like Lee Ann Womack and Billy Joe Shaver. It also left an economic boost as a number of area businesses benefitted from the influx of Warren County visitors.“The Autumn Street Fair is usually our biggest weekend of the year, but this weekend beat that,” said Collins River BBQ co-owner Hannah O’Neal.