Most listings are in the $10's per square foot per year. The Keller region is going through a decrease in rates. In the last 3 months, the median rate decreased $3 per sqft per year. That's a 13% decrease in rent.
Compared to the rest of the DFW Metroplex market, the Keller region has lower rates, so you should have no trouble finding a great deal in this depreciated submarket.
In the last 90 days, 3 listings have come on the market, which means listings most likley are leasing quickly. You'll want to be prepared to tour spaces as quick as possible. 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 2,070 sqft. Most buildings in this region are approximately 1 floors. Most buildings in this region were built in 2006 and are Class B.