That one song made him seriously rich. He's one of the most financially successful in his genre. There are 30 or so Margaritaville restaurants around the world, even cruises with that theme. I read that he gets 6 figures to do private parties. Nice work if you can get it.
He's a good performer. I always liked this song (written by Jesse Winchester):
https://www.youtube.com/watch?v=OsrxNAZCY6Q