Entry fees in tournaments can vary, either requiring diamonds or coins as currency. The specific entry fee depends on the nature of the tournament and what you are racing for.
Tournaments created for coins and diamonds offer players who may not have the resources or time to earn and upgrade their bikes a chance to progress faster in the game.
Certain tournaments offer real-world prizes that can be worth over $600, and for such tournaments, the entry fee is typically in diamonds.
Each time you participate in a tournament, you will spend the currency indicated on the entry fee button. For instance, if the entry fee is 5 diamonds, every race you compete in will cost you 5 diamonds.
To clarify, each time you participate in a tournament, an entry fee will be charged.