You could try Coinbase but if you don't have an account already with them it could take several days. You would need to provide them with identification and link to your bank account. If you are willing to do this, then it's relatively easy to sell through them in my experience.

Once you get all that set up, you put in a sell order and they deposit to you bank in a couple of days. I recommend doing a small sell first to make sure there are no problems. I also don't know if I would sell a lot at one time. I would suggest doing it over the course of a few months to a year or more if you are cashing out that much.