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 increased $1 per sqft per year. That's a 4% rise in rent.
Compared to the rest of the East Bay market, the Brentwood region has smaller rates, so you should have no trouble finding a great deal in this depreciated submarket.
In the last 90 days, 15 listings have been posted online, which means spaces most likley are going fast. You'll want to be prepared to tour spaces as quick as possible. About 7% of the listings in the Brentwood are subleases, so you will probably need to consider the implications of signing a direct lease with the building. 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 1,990 sqft. Most buildings in this area are close to 1 floors. Most buildings in this market were built in 2003 and are Class A.