According to an article in today's WSJ the gay marriage ban is costing San Francisco $37.2 million a year and the state $490 million over three years. These statistics are based on estimates of lost revenue and taxes the state would have received from same-sex marriages during that time.
This seems like a drop in the bucket for a state facing a $20 billion budget gap, but it is yet again another interesting argument against prop 8 and one that has financial implications - probably disproportionately for Northern CA and the SF bay area.
I concur with Dr. Levy of the Center for Continuing Study of the California Economy who says in the article that the greatest potential cost could be to the state's reputation as a haven for all people. "If we do something that makes them feel unwelcome compared to other places they might live, we'll lose talent." To that I'd like to say, "Yes" and "Welcome to MA" where same-sex marriage has been legal for years.