You have no choice but to use P2P or a bitcoin ATM since this is more likely to have lower fees than if you chose the bank. Though P2P is very difficult as you need to find the right person on it and it is very risky as you are transacting huge amounts of money, either you get scammed or robbed. Bitcoin ATMs are good, but i think there is a limit on them and there are fees, but I think they are way less than the banks. But again, you are not planning to sell it right now? It is still in the future, so it is more likely you will have other choices in the future; just don't think of it just yet.