I suggest, to everyone, that they contact Maureen Hunter at MB Services. Gas Valves is what they do. It is streamlined and efficient. They use a different type of valve (excess flow) which is far less problematic than the only slightly less expensive vibration style shut off valve (trucks etc can easily trip them and then you have to reset and relight).
I am providing this info because I am very happy with their products and service which equates to happy clients.
Here is the info from MB Services;
As of March 11th the new "model" Contra Costa County ordinance for gas shut off valves in unincorporated areas of Contra Costa at point of sale became effective. This eliminates the neccessity to install the internal gas appliance valves. The requirement is a shut off valve at the gas meter and a permit. Our cost, depending on the gas flow/BTU's into the home should range from $485.00 to $585.00. Please call with any questions, request for quotes or to order an installation.