The typical asking rate per listing is in the $20's per square foot per year. The Brentwood submarket is going through a a boost in rates. In the last 3 months, the median rate rose $5 per sqft per year. That's a 23% increase in rent.
Compared to the rest of the East Bay market, the Brentwood submarket has lower rates, so you should have no trouble finding a great deal in this depreciated region.
In the last 90 days, 5 listings have been posted online, which means new listings are probably leasing quickly. You'll want to be prepared to tour spaces as quick as possible. About 20% of the listings in the Brentwood 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 available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 500 sqft. Most buildings in this area are close to 1 stories. Most buildings in this area were built in 2003 and are Class A.