Dude! I don't know what the CA rate is now, but here in FL a few years ago it was $125.
Typically, homeowners insurance is rated at the lower of first mortgage balance or replacement cost of the structure. Most of the time the first mortgage value is higher than the estimated per sq ft replacement cost so insurance agents don't have to bother.
A decent agent should know this number for your area. It's not that hard to figure out. Look at new construction prices, deduct land value as estimated by property appraiser, calculate per sq foot cost.