None, but you have to have knowledge and experience in martial arts
You need to be very good at fighting/ martial arts. You also need to have a very tough and calm mentality.
You can't be a fighter without experience, it's one of the most valuable things you can have
It's about 12-50 thousand dollars
Advantages and disadvantages
You can fight for money, but it's not that much money. You get the title of best fighter in the world. Downside like in any sport you could die/ get injured.