The typical asking rate per listing is in the $0's per square foot per year. The San Anselmo region is seeing a decrease in rates. In the last 3 months, the median rate fell $40 per sqft per year. That's a 100% decline in rent.
In the last 90 days, 6 listings have been posted online, which means leases are probably going fast. You'll want to be prepared to make an offer immediately. 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 sqft. Most buildings in this area were built in 1962 and are Class B.