You can look at the cost of living index in those cities.

Use as your base (100), cost of living index is 126.811, LA is about 119.687. Your $78,000/yr salary in is equivalent to $61,509 in , $65,170 in LA, respectively.

Those indices were correct. The cost of living is more expensive in San Jose and LA than in Seattle.

Forgot to congratulate you on getting your offer! Best of luck to you!