The typical asking rate per listing is in the $20's per square foot per year. The Longfellow submarket is going through a an increase in rates. In the last 3 months, the median rate rose $26 per sqft per year.
In the last 90 days, 8 listings have been posted online, which means new availabilities most likley are leasing quickly. You'll want to be prepared to tour spaces as quick as possible. 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 1,900 sqft. Most buildings in this region were built in 1974.