On average, listings lease in the $20's per square foot per year. The Santa Rosa submarket is seeing a an increase in rates. In the last 3 months, the median rate went up $2 per sqft per year. That's a 7% rise in rent.
Compared to the rest of the Bay Area market, the Santa Rosa region has smaller rates, so you should have no trouble finding a great deal in this depreciated region.
In the last 90 days, 36 listings have been posted online, which means leases most likley are leasing quickly. You'll want to be prepared to tour spaces as quick as possible. 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 1,300 sqft. Most properties in this market are around 2 floors. Most buildings in this market were built in 1982 and are Class B.