Most listings are in the $20's per square foot per year. The Petaluma submarket is experiencing a decline in rates. In the last 3 months, the median rate decreased $4 per sqft per year. That's a 14% decrease in rent.
Compared to the rest of the Bay Area market, the Petaluma region has smaller rates, so you should have no trouble finding a great deal in this discounted region.
In the last 90 days, 60 listings have been made available, so you'll want to check back regularly for new listings. About 2% of the listings in the Petaluma are subleases, so you will probably have to consider a longer term lease. There aren't many listings below 2,000 square feet available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 2,200 sqft. Most buildings in this area are approximately 1 stories. Most buildings in this area were built in 1990 and are Class A.