Most listings are in the $10's per square foot per year. The Mendocino submarket is experiencing a a rise in rates. In the last 3 months, the median rate went up $17 per sqft per year. That's a Inf% increase in rent.
In the last 90 days, 4 listings have been made available, which means listings most likley are 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 740 sqft. Most buildings in this area are around 1 stories.