Most listings are in the $10's per square foot per year. The Missoula submarket is going through a decline in rates. In the last 3 months, the median rate fell $3 per sqft per year. That's a 15% decline in rent.
In the last 90 days, 62 listings have been posted online, so you'll want to check back regularly for new listings. About 24% of the available leases in the Missoula are subleases, so you might be able to find a shorter term or below market rent. 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 2,050 sqft. Most buildings in this area are around 2 stories. Most buildings in this area were built in 1971 and are Class C.