The typical asking rate per listing is in the $20's per square foot per year. The Green Park region is going through a a boost in rates. In the last 3 months, the median rate increased $22 per sqft per year.
In the last 90 days, 15 listings have been made available, which means office spaces are probably going fast. You'll want to be prepared to tour spaces as quick as possible. About 7% of the listings in the Green Park are subleases, so you will probably have to consider a longer term lease. 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 1,200 sqft. Most buildings in this area are close to 2 floors. Most buildings in this market were built in 1985 and are Class B.