Using your text editor, alter the "championship.ini" file in the "\RC Cars\script" folder. In the "Upgrades" heading and change the "RaceTariff (int)" value to any desired low number.
Cheaper tracks
Using your text editor, alter the "championship.ini" file in the "\RC Cars\script" folder. In the "Level Information" heading and change the "AccessCash (int)" value to "0". Any track can now be unlocked for free.
Free race fee
Using your text editor, alter the "championship.ini" file in the "\RC Cars\script" folder. In the "Level Information" heading and change the "RaceTariff (int)" value to "0". Any track can now be raced on for free.
Higher prize
Using your text editor, alter the "championship.ini" file in the "\RC Cars\script" folder. In the "Level Information" heading and change the "Place1 (int)", "Place2 (int)", or "Place3 (int)" value to the desired amount of winning money.
More cars
Using your text editor, alter the "championship.ini" file in the "\RC Cars\script" folder. In the "Cars Information" heading and change the "IsEnabled (int)" value for the desired car to "1".
More tracks
Using your text editor, alter the "championship.ini" file in the "\RC Cars\script" folder. In the "Level Information" heading and change the "IsOpened (int)" value for the desired track to "1".
Start with more money
Using your text editor, alter the "championship.ini" file in the "\RC Cars\script" folder. In the "Car Codes" heading and change the "DefaultCash (int)" value to a higher amount to start with that much money.
Cheap upgrades...