Compared to the rest of the Bay Area market, the San Anselmo submarket has greater rates, and you'll need to make a great offer to be in this hot region.
In the last 90 days, 2 listings have come on the market, which means leases are probably going fast. You'll want to be prepared to tour spaces as quick as possible. There aren't many listings below 2,000 square feet available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,200 sqft. Most buildings in this area were built in 2004 and are Class B.