yea I think OP needs to clarify which segment he is going after. You should have an idea of what specific car you want first too, instead of picking a place and using that to filter what they have there.
1) does he wants a 2 to 3 year old car that just came off of lease, and likely CPO'ed or with a year or two of warranty left.
This should be a near perfect car, with minimal or even included maintenance for a couple years.
2) does he want to minimize costs and get a 4 or 5year old car. private party, no warranty, possibly some outstanding maintenance. Older car may have a major due.
OP is in California, so yes it's better to buy in california. If he were out of state, it doesn't make sense to buy in CA and ship out. And vice versa, if he buys out of state better be sure it's a no tax state otherwise will have to pay double, when he brings it back and has to pay sales tax on it again to register.
That being said, I recently bought a car, and found that cargurus.com worked really well to get an idea of what is out there and what I was looking for, basically by providing a market price right there so you don't need to cross compare and keep entering things into kbb or other pricing site open at the same time.
Doublecheck the numbers though, some of their pricing advice is way off though as some dealers may miscategorize their car by a year or by trim.
Your best bet in CA is either going to be in LA area for south or in SF BayArea for north.
It depends on what you decide you want, then basically you have to find the volume dealer for that brand who wants to turn over cars. Or you may find the exact one you want and just go and inquire there.
You should verify any maintenance or warranty extension you might be interested in is going to be honored by your local dealer without a lot of red tape.
At worse, most of the dealers are in networks, so they could charge you perhaps $500 to ship a car in from somewhere else. If the exact car you want is in the armpit of CA, and not worth making a vacation of it htere, $500 can get it to somewhere else.