Trulia: There is no such thing as a "typical cost" for Earthquake insurance for renters in CA, because the price is dependent on where they live geographically, what kind of structure they occupy (wood, concrete, or steel), and how much they choose to insure (limits).
When considering Earthquake insurance, it's important to understand what you are paying for:
only two major hazards - collapse (your things are crushed and burried in rubble), and breakage
(your things are broken - a peril not covered under basic insurance forms).
The cost of Earthquake insurance is complicated by generally very large deductible of 15% not of
your loss, but of the amount of your coverage, together with expensive annual premiums. Of course
any premiums, and deductible you pay will look like a bargain when compared with a total loss of
all you own, but FEAR should motivate education and wise action, not simply trigger an emotional
purchase that may be of little to no benefit to you.
California Department of Insurance statistics seem to suggest that fewer than 15% of all Californians purchase Earthquake insurance, so if you don't have it, you're in the majority. That
alone does not mean you've made the wisest decision for yourself.
Opinions you get from different insurance agents may be biased, I hope mine is not. I think much
depends on the individual, their finances, what they own, where they live, etc. so what's right for one
may not be for you.