Most listings are in the $10's per square foot per year. The Exton submarket is seeing a a rise in rates. In the last 3 months, the median rate rose $18 per sqft per year.
In the last 90 days, 1 listings have been posted online, which means office spaces most likley are going fast. You'll want to be prepared to make an offer immediately. About 100% of the available leases in the Exton 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 available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 2,330 sqft. Most properties in this market are around 2 stories. Most buildings in this region were built in 1970 and are Class B.