Most listings are in the $10's per square foot per year. The Sumner submarket is going through a decline in rates. In the last 3 months, the median rate fell $47 per sqft per year. That's a 71% decrease in rent.
Compared to the rest of the Seattle Metropolitan Area market, the Sumner region has lower rates, so you should have no trouble finding a great deal in this undervalued submarket.
In the last 90 days, 6 listings have been listed, which means listings might be going fast. You'll want to be prepared to make an offer immediately. There aren't many listings below 2,000 square feet on the market, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,120 sqft. Most buildings in this area are close to 2 floors. Most buildings in this market were built in 2001 and are Class B.