Most listings are in the $0's per square foot per year. The Center City East submarket is going through a decline in rates. In the last 3 months, the median rate fell $36 per sqft per year. That's a 100% decrease in rent.
In the last 90 days, 16 listings have been listed, which means leases are probably leasing quickly. You'll want to be prepared to make an offer immediately. 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 sqft. Most properties in this market are around 5 stories. Most buildings in this area were built in 1924 and are Class A.