^I agree. Buying a house in California will negate the in-state rate unless you plan on living in one of the smaller, less expensive farming communities, or in some not so safe neighborhoods, but jobs may not be plentiful in those communities.
FYI: Some rents are more expensive than mortgages. Additionally, transportation costs and commutes are not good.
I agree with the above posters that expecting to be an in-state resident in order to try to gain admission into a UC is a risk. If you’ve already promised your son this future, then I suggest you have a discussion about speaking too soon about a guarantee.