Welcome to College Confidential, @CatFam!
Will your family be able to contribute anything out of annual earnings toward college, or is your son’s budget $20k/year?
Do you qualify for any of the California grant programs? @Gumbymom can hopefully share more, but if you don’t, I’m not sure if the UCs will be affordable.
I am not a math expert, but this thread might be of interest. It was for a student who was also interested in pure math (and from CA, to boot)! Help find math heavy colleges for math head (jr)?
I’m also going to page @Twoin18 who can probably provide some great advice for you.
And as one option to consider, think about the U. of Utah. It’s a WUE school, but it also allows students to get in-state residency if they stay for 12 consecutive months (so stay for a summer in addition to the school year). That could end up making it an affordable option to consider.