Most listings are in the $30's per square foot per year. The Petaluma submarket is seeing a an increase in rates. In the last 3 months, the median rate went up $34 per sqft per year.
Compared to the rest of the Bay Area market, the Petaluma submarket has lower rates, so you should have no trouble finding a great deal in this discounted region.
In the last 90 days, 31 listings have come on the market, which means new listings most likley are going fast. You'll want to be prepared to make an offer immediately. About 55% of the available space in the Petaluma 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.
The standard measurement for office space in this area is around 1,580 sqft. Most buildings in this area are around 2 stories. Most buildings in this area were built in 1996 and are Class A.