Most listings are in the $0's per square foot per year. The Mill Valley submarket is going through a decline in rates. In the last 3 months, the median rate fell $51 per sqft per year. That's a 100% decrease in rent.
In the last 90 days, 11 listings have come on the market, which means new listings are probably leasing quickly. You'll want to be prepared to tour spaces as quick as possible. There aren't many listings below 2,000 square feet on the market, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around sqft. Most properties in this area are around 2 floors. Most buildings in this region were built in 1964 and are Class A.