On average, listings lease in the $40's per square foot per year. The Tamalpais-Homestead Valley submarket is experiencing a a boost in rates. In the last 3 months, the median rate increased $3 per sqft per year. That's a 6% rise in rent.
Compared to the rest of the Bay Area market, the Tamalpais-Homestead Valley submarket has greater rates, and you'll have to negotiate above asking rent to be in this hot region.
In the last 90 days, 5 listings have been listed, 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 1,270 sqft.