Most listings are in the $20's per square foot per year. The Castle Rock submarket is experiencing a decline in rates. In the last 3 months, the median rate decreased $3 per sqft per year. That's a 11% decline in rent.
Compared to the rest of the Denver Metro market, the Castle Rock region has lower rates, so you should have no trouble finding a great deal in this discounted region.
In the last 90 days, 15 listings have been listed, which means office spaces most likley are going fast. You'll want to be prepared to make an offer immediately. About 7% of the available leases in the Castle Rock are subleases, so you will probably have to focus your search on direct office leases. 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 2,030 sqft. Most buildings in this region are around 2 floors. Most buildings in this region were built in 1993 and are Class B.