Most listings are in the $10's per square foot per year. The Duncanville region is going through a a boost in rates. In the last 3 months, the median rate went up $16 per sqft per year.
Compared to the rest of the DFW Metroplex market, the Duncanville submarket has lower rates, so you should have no trouble finding a great deal in this undervalued region.
In the last 90 days, 4 listings have been posted online, which means new availabilities are probably going fast. You'll want to be prepared to tour spaces as quick as possible. About 25% of the office spaces in the Duncanville 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 available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,400 sqft. Most buildings in this market are around 1 stories. Most buildings in this region were built in 1989 and are Class A.