Most listings are in the $20's per square foot per year. The Mansfield submarket is going through a a boost in rates. In the last 3 months, the median rate rose $5 per sqft per year. That's a 33% increase in rent.
Compared to the rest of the DFW Metroplex market, the Mansfield region has lower rates, so you should have no trouble finding a great deal in this discounted submarket.
In the last 90 days, 7 listings have been listed, which means spaces 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 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 2,460 sqft. Most buildings in this area are around 1 stories. Most buildings in this area were built in 2006 and are Class B.