On average, listings lease in the $20's per square foot per year. The Brentwood region is seeing a a rise in rates. In the last 3 months, the median rate went up $24 per sqft per year.
Compared to the rest of the East Bay market, the Brentwood region has less expensive rates, so you should have no trouble finding a great deal in this depreciated region.
In the last 90 days, 5 listings have come on the market, which means leases might be going fast. You'll want to be prepared to make an offer immediately. 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 1,520 sqft. Most buildings in this market are around 1 floors. Most buildings in this market were built in 2003 and are Class A.