I am currently living in Los Angeles, but will be moving back to Texas
in a few months. I need to buy a used car before I move back to Texas.
I've been told that I should just buy the car in Texas to avoid paying
taxes twice, registration twice and all the fees that CA charges.
I also have to consider the $100 plane ticket back to TX to buy the
car and then the gas etc to drive back to CA.
I'm trying to figure out the best option based on $$$$. Can you help
with any advice?

Buy it in Texas.  Buy it online to save the price of a ticket.  Have
the dealer send it to an independant mechanic whom you can pay to
check out the car and make sure everything is okay.  Or if it's a new
car you don't have to worry about it.