On average, listings lease in the $10's per square foot per year. The Sumner submarket is seeing a decline in rates. In the last 3 months, the median rate decreased $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 smaller rates, so you should have no trouble finding a great deal in this depreciated region.
In the last 90 days, 6 listings have been listed, which means new listings are probably 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 around 2 stories. Most buildings in this area were built in 2001 and are Class B.