The typical asking rate per listing is in the $30's per square foot per year. The Napa submarket is experiencing a a rise in rates. In the last 3 months, the median rate rose $1 per sqft per year. That's a 3% rise in rent.
In the last 90 days, 16 listings have been posted online, which means office spaces 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 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 1,320 sqft. Most buildings in this area are close to 1 stories. Most buildings in this area were built in 1980 and are Class A.