On average, listings lease in the $20's per square foot per year. The Chester County submarket is going through a a boost in rates. In the last 3 months, the median rate increased $5 per sqft per year. That's a 18% rise in rent.
In the last 90 days, 95 listings have come on the market, so you'll want to check back regularly for new listings. About 2% of the listings in the Chester County are subleases, so you will probably need to consider the implications of signing a direct lease with the building. 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 2,470 sqft. Most properties in this region are approximately 2 floors. Most buildings in this area were built in 1986 and are Class B.