Most listings are in the $20's per square foot per year. The Duncanville submarket is seeing a a boost in rates. In the last 3 months, the median rate rose $2 per sqft per year. That's a 10% rise in rent.
Compared to the rest of the DFW Metroplex market, the Duncanville region has lower rates, so you should have no trouble finding a great deal in this depreciated region.
In the last 90 days, 4 listings have come on the market, which means new listings most likley are going fast. You'll want to be prepared to make an offer immediately. 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 1,000 sqft. Most properties in this market are close to 1 stories. Most buildings in this area were built in 1989 and are Class A.