Most listings are in the $10's per square foot per year. The Dover region is going through a an increase in rates. In the last 3 months, the median rate increased $20 per sqft per year. That's a Inf% increase in rent.
Compared to the rest of the Greater Boston market, the Dover submarket has lower rates, so you should have no trouble finding a great deal in this discounted region.
In the last 90 days, 4 listings have come on the market, which means listings 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 posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,460 sqft. Most properties in this region are approximately 2 floors. Most buildings in this area were built in 1902 and are Class Class B.