Most listings are in the $50's per square foot per year. The Mill Valley submarket is experiencing a a rise in rates. In the last 3 months, the median rate increased $0 per sqft per year. That's a 1% rise in rent.
Compared to the rest of the Bay Area market, the Mill Valley submarket has greater rates, and you'll need to pay a premium to be in this hot region.
In the last 90 days, 11 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 posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 570 sqft. Most properties in this region are approximately 2 stories. Most buildings in this market were built in 1964 and are Class A.