Yes, quite expensive. As a non-resident, you'll be hit with higher tuition fees. For the California State Universities that means $ 2,724 plus $ 282 per semester unit (assuming Full Time enrollment). For the Univ. of California it translates to $ 6,780 plus a flat $17,820 (Full Time, not calculated by unit -- but still far more expensive than the former when you do the math).
It's also important to secure housing very early in the process. If you want to live alone, you're looking at 800-1,400 for a studio or 1,200-1,800 for a one bedroom (here in San Fran, for instance). So it's better to have roommates and split the costs.
Now, I don't want to dissuade you because Calif. does indeed have great universities. And it's a great place to be - very vibrant, cosmopolitan, and diverse. After all, Los Angeles and San Francisco are world famous cities for good reason. But do consider your resources and plan carefully.