Choose a car you wish to gamble for but do not
press "Gamble" yet. Instead, remove your memory
card, then press "Gamble". You will be asked if
you are sure. Select "OK", then the
message "Autosave has been disabled" will
appear. Select "Continue without autosave". If
you lose the race, reset your Gamecube, insert
the memory card, and you will still have the
money. If you win, put the memory card back in
after the race, then go to options and autosave.
Select "Overwrite file", and you will be able to
save the car again.