Most listings are in the $20's per square foot per year. The Portsmouth region is going through a decrease in rates. In the last 3 months, the median rate decreased $2 per sqft per year. That's a 8% decrease in rent.
Compared to the rest of the Greater Boston market, the Portsmouth submarket has lower rates, so you should have no trouble finding a great deal in this depreciated region.
In the last 90 days, 64 listings have been made available, so you'll want to check back regularly for new listings. About 28% of the office spaces in the Portsmouth are subleases, so you might be able to sign a shorter term by taking over a previous lease. 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 2,200 sqft. Most properties in this area are around 2 floors. Most buildings in this market were built in 1930 and are Class A.