On average, listings lease in the $20's per square foot per year. The Renton submarket is going through a a rise in rates. In the last 3 months, the median rate rose $1 per sqft per year. That's a 3% increase in rent.
Compared to the rest of the Seattle Metropolitan Area market, the Renton submarket has less expensive rates, so you should have no trouble finding a great deal in this undervalued region.
In the last 90 days, 18 listings have been made available, which means new listings 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.
Even though the median size is 4,990 sqft, there are still 0 office spaces below 2,000 sqft. Most buildings in this market are around 2 stories. Most buildings in this area were built in 1983 and are Class A.