The typical asking rate per listing is in the $20's per square foot per year. The Thornton region is going through a a rise in rates. In the last 3 months, the median rate rose $5 per sqft per year. That's a 22% rise in rent.
Compared to the rest of the Denver Metro market, the Thornton region has less expensive rates, so you should have no trouble finding a great deal in this discounted submarket.
In the last 90 days, 12 listings have been made available, which means office spaces are probably going fast. You'll want to be prepared to tour spaces as quick as possible. 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 1,460 sqft. Most properties in this market are around 2 stories. Most buildings in this area were built in 1986 and are Class B.