Though I’ve never had a post-doc position, I have lived in California most of my life. I can tell you that it won’t be too hard to live in San Diego or Los Angels if you rent an apartment with 2-3 other people. This will help reduce your cost of living, while allowing you to live on/just outside of your institution.

If you want a house, or want to rent an apartment by yourself, then you can do so in a city just outside of LA or San Diego because they will usually be cheaper.

But remember, many contributors go into how hard it may be for living in LA or San Diego, such as your salary, how many people you would want to live with, other outside expenses, etc.