I have taken the Disneyland express before and it worked just fine.
Another option that I have used is a rental car. I rented from Hertz at LAX and made my reservation so that I could drop the car at the HLE (Hertz Local Edition) right by Disneyland. That way, I only had to pay for one day of rental. It also made it so that I could drive to a grocery store and pick up a few items to cut down the price of food. When you drop off your car, Herts will run you back to the park or a nearby hotel. I then played at Disneyland for however long we stayed. To get back to LAX, we had made another reservation from the HLE to LAX. Hertz coordinated a pickup time and place. I just paid for another one day rental and drove back to LAX.
I haven't heard of many other people trying this, but it may work well for you. I believe there is an Enterprise (The evil E), or National/Alamo right by Disneyland too. Hertz specializes in one way rentals, so I went with them.