On average, listings lease in the $20's per square foot per year. The New Hampshire submarket is going through a a boost in rates. In the last 3 months, the median rate increased $1 per sqft per year. That's a 3% rise in rent.
In the last 90 days, 1500 listings have come on the market, so you'll want to check back regularly for new listings. About 1% of the listings in the New Hampshire are subleases, so you will probably have to focus your search on direct office leases. 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 1,850 sqft. Most buildings in this region are close to 2 stories. Most buildings in this market were built in 1950 and are Class Class B.