just across the street from the cruisehship terminal, there is an Enterprise Rent a Car office. I think the address is something like 500N Harbor Blvd, look it up on the Enterprise website.
I have rented a car from them numerous times after we return from cruises and they have always been nice enough to waive the drop-off charge. I usually rent the cheapest car, around $20 for a day.
That may be on easy and inexpensive way to get to LAX!
On the other hand, Super Shuttle will cost you approx $30 each to LAX.
Hope that helps
oh, btw, they will also pick you up from the cruiseship terminal if you haev a reservation