Based on the answer received from Pamela Koslyn:
Since your spouse can argue he contributed to house payments, upkeep, etc., during the marriage and is entitled to some interest in in, you may want a pre-nuptual agreement to protect your property that he'd otherwise be entitled to.
To get the going rates are for family lawyers in San Francisco, make a few phone calls to lawyers there. For referrals to SF family lawyers, call your local bar associations or do internet searches.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.