Most listings are in the $10's per square foot per year. The Wilmington region is experiencing a a rise in rates. In the last 3 months, the median rate rose $16 per sqft per year.
In the last 90 days, 4 listings have been listed, which means new listings most likley are going fast. You'll want to be prepared to make an offer immediately. About 25% of the available leases in the Wilmington 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 on the market, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 2,000 sqft. Most buildings in this area were built in 2006.