There isn't really a salary. All you do is sign a paper that says you are going to fight someone for X amount of dollars. Holmes made $63 in his first fight, but that was in 1973, and even then it was pretty low. I would say the average heavyweight makes about $200-$300 his first few fights, then there is usually 1 big fight, and that will either make you, or break you. With Holmes it was with Roy Williams. After you win that one big fight, it puts you on the charts, and promoters start paying attention for you, and if you win the title, its almost a given you will make a million or 2.