I guess how expensive it would be to retrofit a home would be based on many factors. I remember reading one story after the Northridge quake about a home that was destroyed by the quake in Santa Clarita that, because the house was on top of a hill, had to drill down several hundred feet in order to have a strong foundation support. I can't remember all the terms that were used, but it was expensive.

Another story is when I lived in a condo, the board had voted to not obtain earthquake insurance. The reasoning was that most people would just walk away from the condo instead of trying to rebuild it.