The typical asking rate per listing is in the $20's per square foot per year. The Missoula region is going through a an increase in rates. In the last 3 months, the median rate went up $2 per sqft per year. That's a 10% increase in rent.
In the last 90 days, 62 listings have come on the market, so you'll want to check back regularly for new listings. 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 2,270 sqft. Most properties in this region are close to 2 floors. Most buildings in this market were built in 1971 and are Class C.