Originally, some buses were locked behind real-money DLCs. However, the developers stated their intention to make many DLC buses purchasable with in-game currency. If you have a legitimate copy, using the Garage Money Cheat
The developers, KishMish Games, frequently offer steep discounts or free updates: bus driver simulator 2019 dlc unlockerplaza best
If you are deciding which content to prioritize, these are considered the best additions to the game: Originally, some buses were locked behind real-money DLCs