Most listings are in the $30's per square foot per year. The Petaluma region is going through a an increase in rates. In the last 3 months, the median rate rose $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 undervalued submarket.
In the last 90 days, 31 listings have come on the market, which means new listings might be going fast. You'll want to be prepared to tour spaces as quick as possible. About 65% 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 properties in this area are around 2 floors. Most buildings in this region were built in 1996 and are Class A.