It's called a cashless exercise. You exercise and sell the stock right away so you don't need to have the money to buy. However the problem is most startups in

It's called a cashless exercise. You exercise and sell the stock right away so you don't need to have the money to buy. However the problem is most startups in this case are not liquid so you cannot sell your shares (with some exceptions). Google and other public companies give you direct shares via RSUs since they can sell part of your shares to cover the taxes.