Find a car you want, but can’t afford. Now, leave the game. Find the name of the car you want and look up the relevant .txt file on disk 2 (e.g. if you wanted an Escort, you would find Escort.txt). Now use a text editor (I use TXED) and find a number (at the beginning). It should look something like 00000012345.
Now, fill in the places where the 12345 # is with 0s in their place. Now just leave a trailing 1. Now the car will cost all of $10. This is not only a way to get the car you want, but makes it cheaper to just buy a new car each time instead of refuelling/fixing damage.