The typical asking rate per listing is in the $70's per square foot per year. The Larkspur submarket is going through a a rise in rates. In the last 3 months, the median rate rose $4 per sqft per year. That's a 6% rise in rent.
Compared to the rest of the Bay Area market, the Larkspur submarket has higher rates, and you'll have to negotiate above asking rent to be in this hot submarket.
In the last 90 days, 6 listings have been posted online, which means leases most likley are going fast. You'll want to be prepared to make an offer immediately. About 33% of the available leases in the Larkspur are subleases, so you might be able to find a shorter term or below market rent. 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 1,980 sqft. Most buildings in this region are around 2 stories. Most buildings in this region were built in 1980 and are Class B.