On average, listings lease in the $10's per square foot per year. The Union City region is going through a decrease in rates. In the last 3 months, the median rate fell $6 per sqft per year. That's a 26% decline in rent.
Compared to the rest of the East Bay market, the Union City submarket has lower rates, so you should have no trouble finding a great deal in this undervalued region.
In the last 90 days, 5 listings have been posted online, which means leases most likley are going fast. You'll want to be prepared to make an offer immediately. 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 2,500 sqft. Most buildings in this region are around 1 floors. Most buildings in this region were built in 1987 and are Class A.