Using this method, you can get the elite king's car twice. This method only works on kings you haven't defeated. First enter the cheat unlockallthings at the code entry menu at the career
main menu Then let it save and reload your career. You should have unlocked all race days. Fight the king you want (for this guide,i'm going to use the drag king) after you win, let it save, get your reward, let it save again and reboot your ps2. Then race in the race days the king you fought against belong to (eg. if you raced karol monroe, race at the rogue speed race days)
Keep dominating the races, and you will be challenged again by the king you raced before. Win the race and you will get their car again!