Los Angeles International Airport: For the cheapest sensible transfer, take Big Blue Bus Route 3 from the LAX/Metro Transit Center to Downtown Santa Monica/4th Street: roughly 43 minutes once aboard, usually every 15 minutes, about $1.25 with TAP/mobile ticket ($1.50 cash). Allow 60–90 minutes airport-to-hotel after the airport connection and luggage. A rideshare is the better choice late at night or with several people, but traffic can make a nominally short trip take 45–75 minutes and fares surge.
Downtown Los Angeles / LA Union Station: Use Metro’s E Line (the former Expo Line) to Downtown Santa Monica, at 4th Street and Colorado Avenue, a few blocks from the Pier. From Union Station, connect via downtown Metro service; from central LA, the E Line is usually preferable to a taxi during peak traffic. Metro fare is about $1.75.
Santa Monica Airport: This is a general-aviation/business-jet airport, not a commercial-arrival option. It is in southern Santa Monica; a short rideshare or Big Blue Bus connection reaches downtown, while the airport’s free viewing decks are worth a stop only if you are already nearby.