On average, listings lease in the $10's per square foot per year. The New Castle region is going through a a boost in rates. In the last 3 months, the median rate increased $15 per sqft per year.
In the last 90 days, 0 listings have been posted online, which means leases are probably going fast. You'll want to be prepared to make an offer immediately. About Inf% of the available leases in the New Castle are subleases, so you might be able to find a shorter term or below market rent. 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 1,160 sqft. Most properties in this area are approximately 1 floors. Most buildings in this market were built in 1900 and are Class A.