The typical asking rate per listing is in the $20's per square foot per year. The Chelsea submarket is going through a a boost in rates. In the last 3 months, the median rate rose $22 per sqft per year.
Compared to the rest of the Greater Boston market, the Chelsea submarket has smaller rates, so you should have no trouble finding a great deal in this discounted submarket.
In the last 90 days, 8 listings have been posted online, which means leases most likley are leasing quickly. You'll want to be prepared to make an offer immediately. About 13% of the listings in the Chelsea are subleases, so you might be able to snag a great spot on a short term. There aren't many listings below 2,000 square feet on the market, so finding a space for a small business might be tough.
Even though the median size is 2,570 sqft, there are still 0 office spaces below 2,000 sqft. Most buildings in this area are approximately 2 stories. Most buildings in this area were built in 2001 and are Class B.