Most listings are in the $10's per square foot per year. The Missoula County region is going through a decline in rates. In the last 3 months, the median rate fell $1 per sqft per year. That's a 4% decrease in rent.
In the last 90 days, 8 listings have been posted online, which means new availabilities most likley are leasing quickly. You'll want to be prepared to make an offer immediately. 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 1,750 sqft. Most properties in this market are approximately 1 floors. Most buildings in this market were built in 1981 and are Class A.