renting a car is so much trouble...hire a car services is the way to go so you can relax...
I go to LAX from Irvine often, and I use a sedan svs who picks me up at my home, and greets me by the exit on the way home. It costs $150. They use black extended length sedans.
I use advantage shuttle to go from home to SNA, it is $51. I don't use shuttle svs after landing in SNA. I take the taxi, and it costs only $40, and I don't have to wait by the curb for them to come by.
supper shuttle fare of $48 is for "sharing a van"...which means you have to sit there going to other people's house most of the time. I don't like that and think it takes too long, and not safe - too many people know you are out of town...
The cheapest shuttle svs from Irvine to LAX is by calling a chinese car services company. They charge only $70 for early am pickup, and only 60 for mid day pickups. I never used them before, but talked to their operator. I might consider using them for my next family vacation trip leaving from lax.