On average, listings lease in the $0's per square foot per year. The Cos Cob region is going through a decrease in rates. In the last 3 months, the median rate decreased $46 per sqft per year. That's a 100% decline in rent.
In the last 90 days, 1 listings have been made available, which means listings most likley are going fast. 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 1,850 sqft. Most properties in this area are approximately 3 stories. Most buildings in this area were built in 1967 and are Class A.