Lowest cost carrier iPhone 17 Pro Max

This is a wide open question. It depends upon what service you want. I use a very basic plan that costs me $7 per month but then I make 2 phone calls per month and 3 texts per year. I almost never turn on cellular data.

Remember that this is a word-wide forum and you can probably do the research as easily as we can. Sure, there may be contributors in S. California, but I would not wait for one of them to see your post and reply. There could also be factors that are highly specific to your needs and location. Not all carriers have good signals in any one location.