The typical asking rate per listing is in the $20's per square foot per year. The New Haven submarket is going through a a rise in rates. In the last 3 months, the median rate went up $5 per sqft per year. That's a 20% increase in rent.
In the last 90 days, 19 listings have been listed, which means leases most likley are leasing quickly. You'll want to be prepared to make an offer immediately. About 5% of the listings in the New Haven are subleases, so you will probably need to sign a longer term lease with the landlord directly. There aren't many listings below 2,000 square feet available, so finding a space for a small business might be tough.
Even though the median size is 3,130 sqft, there are still 0 new listings below 2,000 sqft. Most properties in this area are around 3 stories. Most buildings in this area were built in 1926 and are Class A.