Compared to the rest of the Fairfield market, the Cos Cob region has more expensive rates, and you'll have to negotiate above asking rent to be in this hot region.
In the last 90 days, 2 listings have been made available, which means new availabilities are probably going fast. You'll want to be prepared to make an offer immediately. There aren't many listings below 2,000 square feet available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 940 sqft. Most buildings in this area are approximately 3 stories. Most buildings in this region were built in 1967 and are Class A.