This is an interesting topic. I do not think I have ever seen a topic like this before. I think horse racing is probably the most expensive sport. There is a lot of money involved with training the horses, taking care of the horses, and then there is the gambling part of it. Fans all across the world bet money on horse races.
It has to be soccer/football. Every summer and winter millions of dollars are paid for top rated football players around the world. Second thing is that there are maybe more expensive players from other sports but there is no other organized sport with so many players in the world! For example Manchester United costs $3 billion.