The typical asking rate per listing is in the $10'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 increased $17 per sqft per year.
In the last 90 days, 12 listings have been posted online, which means leases are probably leasing quickly. You'll want to be prepared to make an offer immediately. 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 800 sqft. Most properties in this market are approximately 2 stories. Most buildings in this area were built in 1967 and are Class B.