Most listings are in the $30's per square foot per year. The Napa submarket is seeing a decline in rates. In the last 3 months, the median rate fell $2 per sqft per year. That's a 6% decrease in rent.
Compared to the rest of the Bay Area market, the Napa submarket has smaller rates, so you should have no trouble finding a great deal in this undervalued submarket.
In the last 90 days, 24 listings have come on the market, which means new availabilities are probably going fast. You'll want to be prepared to tour spaces as quick as possible. 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 1,400 sqft. Most buildings in this area are approximately 1 stories. Most buildings in this region were built in 1978 and are Class B.