On average, listings lease in the $40's per square foot per year. The Mount Vernon region is experiencing a a boost in rates. In the last 3 months, the median rate rose $26 per sqft per year. That's a 133% increase in rent.
In the last 90 days, 5 listings have been posted online, which means spaces most likley are going fast. You'll want to be prepared to make an offer immediately. About 160% of the available leases in the Mount Vernon are subleases, so you might be able to sign a shorter term by taking over a previous lease. 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 940 sqft. Most buildings in this market are approximately 3 floors. Most buildings in this market were built in 1948 and are Class A.