Unlike many other video games, "Gran Turismo 3: A-Spec" does not have traditional cheat codes, such as a combination of button strokes for a result such as access to unlimited money. Game play strategies and Easter eggs within the game, however, do allow access to special features and enhanced benefits.
One of the fastest and easiest ways to build up a large amount of money from the beginning of game play in "Gran Turismo 3: A-Spec" is to immediately get a license and then get gold qualification on that license. Purchase a vehicle and go to the Sunday Cup race. Repeat this race multiple times to build up a large amount of money to grant access to more advanced vehicles that can participate in races with higher payouts.