Most listings are in the $20's per square foot per year. The Dallas County region is going through a a rise in rates. In the last 3 months, the median rate increased $1 per sqft per year. That's a 5% increase in rent.
In the last 90 days, 1773 listings have been made available, so you'll want to check back regularly for new listings. About 3% of the office spaces in the Dallas County are subleases, so you will probably need to sign a longer term lease with the landlord directly. 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 1,860 sqft. Most buildings in this area are close to 3 floors. Most buildings in this market were built in 1983 and are Class B.