On average, listings lease in the $10's per square foot per year. The Dover region is experiencing a an increase in rates. In the last 3 months, the median rate went up $15 per sqft per year. That's a Inf% increase in rent.
In the last 90 days, 1 listings have been made available, which means spaces are probably leasing quickly. You'll want to be prepared to make an offer immediately. There aren't many listings below 2,000 square feet on the market, 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 area were built in 1934 and are Class C.