The typical asking rate per listing is in the $10's per square foot per year. The Belleville region is going through a decrease in rates. In the last 3 months, the median rate fell $26 per sqft per year. That's a 61% decrease in rent.
In the last 90 days, 5 listings have been made available, which means leases are probably 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 960 sqft. Most properties in this market are approximately 2 stories. Most buildings in this area were built in 1996 and are Class B.