I asked this same question and was recommended SuperShuttle and PrimeTime Shuttle..they both have websites that you can get a quote based on # of passengers..Good luck!
I was the one that asked under the Mexico board. I called Supershuttle and it was 120.00 round trip based on having 5 people. That was being picked up at LAX and taken to LB...and picked up at port and taken back to LAX.