Pro athletes and singers have been wealthy throughout recorded history. Ancient Greek Olympians, poets, actors and singers were very well off, as were there counterparts in Rome. In Rome even slaves who were successful in entertainment would often grow wealthy and earn their freedom eventually. China and Japan also have very old traditions of well off and widely respected entertainers. Even in less well off cultures traveling bards have a tradition of being welcome guests. There are so many examples of entertainers making an excellent living for themselves it's difficult to really source, because I'm not sure how you would source something that is a near constant in both Western and Asiatic societies for thousands of years.