Sell a truck in career mode, then quit the game. Use a text editor to edit
the "metal.ini" file in the "\4x4 evo2\system" folder. Locate the following
lines at the bottom of the file.

careerTruckCount=0
curTruckType=0
Change the "0" to a "1" on both lines, then save the file. Restart the game
and you will still have your truck plus the money that you previously sold 
it for. Repeat this as needed for more money.