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San Diego International Airport is approximately a 1 hour drive from Murrieta, CA and is the easiest airport to fly into. There are several car rental spots in the airport. There is MUCH less traffic than coming from LAX, and it's a beautiful drive! Would recommend this airport, and maybe spending some time in San Diego if you arrive early!
Flight
LAX is on the coast in LA with is approximately 1.5 hours from Murrieta, CA (without traffic). It is often cheaper and more convenient in terms of finding flights. There are multiple car rental options at the LAX airport but expect traffic at most hours of the day when driving to Murrieta. There is plenty to do in the LA and Santa Monica area if you arrive early!
Flight
ONT is approximately 45 minutes from Murrieta, CA. There are a couple of options for car rentals from this airport through Orbitz and other outside companies. There is generally less traffic coming from this airport but it may be difficult to find flights as it is a rather small airport.
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Murrieta does have reasonable Airbnb options! You can use either Murrieta, CA or Temecula, CA as a search option.