Most listings are in the $20's per square foot per year. The King of Prussia region is going through a a rise in rates. In the last 3 months, the median rate rose $24 per sqft per year.
In the last 90 days, 23 listings have been listed, which means new availabilities most likley are going fast. You'll want to be prepared to tour spaces as quick as possible. About 70% of the available space in the King of Prussia are subleases, so you might be able to snag a great spot on a short term. 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 1,780 sqft. Most properties in this region are around 3 floors. Most buildings in this area were built in 1977 and are Class A.