$1 million
Note: A Dreamcast keyboard is required for this code. Use the keyboard in port D. While playing a game, type "goldfinger". If you entered the code correctly, you will hear a sound. Then, type "givememoneyordie". If you entered the code correctly, you will hear a sound. Exit the race and you will have $1 million. Repeating the code will set your current amount to $1 million -- you cannot get more than that amount.

Hidden money
On the Farm Road track, go under the train trestle in the middle of the pond to find $1500.