The typical asking rate per listing is in the $20's per square foot per year. The Renton submarket is going through a a boost in rates. In the last 3 months, the median rate went up $10 per sqft per year. That's a 54% rise in rent.
Compared to the rest of the Seattle Metropolitan Area market, the Renton region has smaller rates, so you should have no trouble finding a great deal in this depreciated region.
In the last 90 days, 11 listings have been listed, which means new listings most likley are leasing quickly. You'll want to be prepared to tour spaces as quick as possible. 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 1,440 sqft. Most properties in this region are close to 2 floors. Most buildings in this area were built in 1983 and are Class A.