Most listings are in the $10's per square foot per year. The Dover submarket is going through a an increase in rates. In the last 3 months, the median rate increased $15 per sqft per year. That's a Inf% rise in rent.
In the last 90 days, 1 listings have been made available, which means leases might be 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 2,020 sqft. Most buildings in this market were built in 1934 and are Class C.