Most listings are in the $30's per square foot per year. The Napa submarket is going through a a rise in rates. In the last 3 months, the median rate increased $33 per sqft per year.
In the last 90 days, 34 listings have been made available, which means new availabilities most likley are going fast. You'll want to be prepared to tour spaces as quick as possible. About 26% of the office spaces in the Napa are subleases, so you might be able to sign a shorter term by taking over a previous lease. There aren't many listings below 2,000 square feet on the market, so finding a space for a small business might be tough.
Even though the median size is 2,990 sqft, there are still 0 leases below 2,000 sqft. Most buildings in this market are close to 1 stories. Most buildings in this region were built in 1983 and are Class A.