The typical asking rate per listing is in the $10's per square foot per year. The Wilmington region is experiencing a an increase in rates. In the last 3 months, the median rate increased $16 per sqft per year.
In the last 90 days, 4 listings have been listed, which means new availabilities are probably going fast. You'll want to be prepared to make an offer immediately. About 25% of the listings in the Wilmington 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 2,000 sqft. Most buildings in this region were built in 2006.