It depends on the house and the city. In LA the retrofit may include Low-Flow toilets, water heater strapping, smoke detectors, Carbon Monoxide detectors, seismic gas shutoff valve, glass retrofitting. The cost for these items vary since each house is different. One house may need new toilets and the next won't. You will need a COC (Certificate Of Compliance) before closing escrow. The retrofitter will provide this. If you want the names of some good retrofitters to call, give me a call.