Most listings are in the $30's per square foot per year. The Castle Rock region is going through a an increase in rates. In the last 3 months, the median rate increased $4 per sqft per year. That's a 14% rise in rent.
Compared to the rest of the Denver Metro market, the Castle Rock region has higher rates, and you'll have to negotiate above asking rent to be in this hot region.
In the last 90 days, 22 listings have come on the market, which means new availabilities are probably leasing quickly. You'll want to be prepared to make an offer immediately. About 5% of the available space in the Castle Rock are subleases, so you will probably have to consider a longer term lease. 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 1,300 sqft. Most properties in this area are approximately 2 floors. Most buildings in this area were built in 1994 and are Class B.