How do you get a new car in burnout paradise demo

Sometimes when you win enough races a car will appear driving around the city. You also get a new car when you upgrade your license you can also buy all the cars you can unlock for free in the game for about ten dollars in the in game if you are to impatient to unlock them all on your own. There are also allot of other cars in the store but some are pretty expensive for just a car on a video game one of the cars is 4.99!! They are outrageously priced in my opinion.

THANK YOU VERY MUCH!!! T___T