You might think it's free but it's not entirely free. For example, it will say show that upon earning 300 stars you can unlock Level Abc. But when you achieve 300 stars, you will see that requirement is changed to 350 star. When you achieve that, it will increase it again. So ultimately you can't play Season 6 without buying a car, because you have already bought all the cars which you could using points. You can only unlock season 6 by paying with money only.