Larger homes, homes with many floor levels, steep hillside homes, and homes with finished basement area rooms, or homes with rooms over garages will cost more to retrofit. In these situations, a complete earthquake retrofit can cost $10,000 or more.nsurance company practices do change. At the time of this writing, the California Earthquake Authority (CEA) which provides the earthquake insurance you receive through many of the major home insurers, will reduce the cost of earthquake coverage by 5% if you have your home retrofitted.