Best place, bar none to stay for the Baja 500 is this place called the Ensenada Beach House Hotel. It is far enough from the main drag that you do not need to worry about being in all the hustle and bustle while you are getting your stuff together. We book here every year and would not consider staying anywhere else. Here is their website -
http://ensenadabeachhouse.com. Rooms are really reasonably priced and its a great atmosphere for the race.
