Most listings are in the $10's per square foot per year. The Rohnert Park region is going through a an increase in rates. In the last 3 months, the median rate increased $17 per sqft per year.
Compared to the rest of the Bay Area market, the Rohnert Park submarket has smaller rates, so you should have no trouble finding a great deal in this depreciated region.
In the last 90 days, 10 listings have been listed, which means new availabilities most likley are going fast. You'll want to be prepared to tour spaces as quick as possible. About 330% of the available space in the Rohnert Park 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 posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,500 sqft. Most properties in this region are close to 2 floors. Most buildings in this market were built in 1985 and are Class B.