Most listings are in the $10's per square foot per year. The Southlake region is going through a a rise in rates. In the last 3 months, the median rate rose $20 per sqft per year.
Compared to the rest of the DFW Metroplex market, the Southlake region has lower rates, so you should have no trouble finding a great deal in this undervalued submarket.
In the last 90 days, 6 listings have come on the market, which means leases are probably going fast. 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 2,000 sqft. Most buildings in this region are around 1 stories. Most buildings in this area were built in 2005 and are Class A.