Most listings are in the $20's per square foot per year. The Spokane Valley submarket is going through a a boost in rates. In the last 3 months, the median rate rose $3 per sqft per year. That's a 14% rise in rent.
In the last 90 days, 17 listings have been listed, which means new availabilities 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 1,630 sqft. Most buildings in this region are close to 2 stories. Most buildings in this area were built in 1982 and are Class B.