Most listings are in the $30's per square foot per year. The Hempstead region is experiencing a a boost in rates. In the last 3 months, the median rate went up $36 per sqft per year.
In the last 90 days, 2 listings have been posted online, which means leases are probably going fast. You'll want to be prepared to tour spaces as quick as possible. About 350% of the available leases in the Hempstead are subleases, so you might be able to find a shorter term or below market rent. 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 700 sqft. Most properties in this market are around 4 stories. Most buildings in this area were built in 1960 and are Class B.