There are car mods to give you what you want. Look for them in the mod list in the Mods section. About the coupon code, as far as I know, the only major discount given officially by the devs is just for owners of the 1.0 version to upgrade to 1.2, the most major update in CCD history, so I'm pretty sure this discount is useless for you

. Of course, like any other place to buy games, there are sales where you can get the game at a cheaper price. All Updates are free, except for 1.2, which came out 2 years ago. Now we're in 1.3.