I'm in NJ so not sure if this applies but since I'm in another high tax state I thought this would be relevant. One thing that I find interesting that isn't really talked about is the difference in property tax rates between different towns. In NJ for example, my parent's home is worth $300k-400k and they pay almost $10k in property taxes per year. Meanwhile, an out of state investor could buy a $3 million property in NJ's Long Beach Island and pay just $30k in property taxes on it (1/3 the rate my parents pay).

I don't know how much this applies to California, I think they cap property tax increases there, not sure how the rates differ by town?

A single state-wide standardized marginal property tax rate would probably work best. Those with $5 million+ single family homes should be paying a higher percentage to discourage that type of housing. Additionally that tax money could be collected at a state level and distributed more equitably (to towns that aren't as wealthy).

Ultimately single family homes need to be phased out in these kinds of places and replaced with higher density along with mixed zoning. Mixed zoning should reduce the need for more car based infrastructure which is extremely expensive and allow more efficient public transit to be built. That would lower costs for regular people since they wouldn't need a car to get places.