On average, listings lease in the $30's per square foot per year. The Napa submarket is experiencing a decline in rates. In the last 3 months, the median rate fell $3 per sqft per year. That's a 7% decline in rent.
Compared to the rest of the Bay Area market, the Napa region has smaller rates, so you should have no trouble finding a great deal in this undervalued region.
In the last 90 days, 13 listings have come on the market, which means leases might be 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 posted, 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 market are around 1 floors. Most buildings in this area were built in 1978 and are Class B.