The main reason for Raoul to go to Las Vegas is to cover the Mint race. When Raol and Dr. Gonzo enter Vegas for the first time and are about to park in front of their hotel there is a banner for the Mint race that says the prize is $100,000. Later in the movie however, when the race begins and dust is flying around there is another banner at the start/finish line only this one says that the prize is now $50,000.