For sport stars, 3-5x expected expenses. Agents, travel, medical, etc... Maybe 8-10x for the top of the top. In America anyway, they make a lot of money with sponsorship and endorsements. I know F1 and other sport driver are putting their lives on the line so they deserve more.
Keep in mind, this comes from a baseball mindset, where the sport is on the downslide and everyone is losing money (except the Yankees and a couple others). So many teams get crushed by bad contracts and light pockets. Salary caps and revenue sharing, between teams and players, needs to be improved. Luxury taxes mean nothing to the Yankees, and to some extent, the Red Sox.
Basketball salaries are just stupid. I don't really have a cogent argument to go along with that statement, it's just how I feel. My only real example is of the power a single player can have to make a team great, ie Michael Jordan, or completely turn it into a disaster, a la Cleveland and LeBron.