Destiny 2 vanilla is like 10$ and you can get year 1 dlc for another 30$ which Includes curse of osiris and warmind dlcs
Forsaken is their taken king-like year 2 dlc, which is another 40$. You dont have to buy the annual pass, but you should if you want the rest of the dlc content released throughout 2019.
They will have bundles like they did for taken king closer to release