LA is a big place. Depends on which area you want to visit. Valley? South Bay? Orange County? Inland Empire?
The easiest airport in LA/OC to visit is Fullerton.
Long Beach has construction going on RWY 25L. I was there last month and stopped at Signature. They only took me for $50 in gas, which was reasonable. Any of the big FBO's is going to take you for some $$$.
Uber and Lyft are easy ways to get around, and very affordable if you don't absolutely need a rental car.