Most listings are in the $20's per square foot per year. The Antioch region is going through a a rise in rates. In the last 3 months, the median rate went up $6 per sqft per year. That's a 31% increase in rent.
Compared to the rest of the East Bay market, the Antioch submarket has less expensive rates, so you should have no trouble finding a great deal in this depreciated submarket.
In the last 90 days, 20 listings have come on the market, which means spaces 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 1,680 sqft. Most properties in this market are close to 1 stories. Most buildings in this area were built in 1989 and are Class C.