Make a backup of the Carma.pak file in the assets folder. Then open the file in wordpad. scroll down to the part that starts:

ENDDIFFICULTY

Here you will find the attributes for Ped_Credits / Checkpoint_credits and the like ...add a few zeros to the numbers and remove the line APO_TRADE_OFFENSIV that is at the bottom of this part of the text or else the hack won't work. This hack will make it nice and easy to score credits and afford all the cars.