On average, listings lease in the $20's per square foot per year. The Missoula County submarket is going through a a boost in rates. In the last 3 months, the median rate rose $2 per sqft per year. That's a 13% rise in rent.
In the last 90 days, 4 listings have been made available, which means leases most likley are going fast. 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 1,940 sqft. Most properties in this region are approximately 2 floors. Most buildings in this market were built in 1981 and are Class A.