On average, listings lease in the $20's per square foot per year. The Tukwila region is going through a a rise in rates. In the last 3 months, the median rate increased $13 per sqft per year. That's a 83% rise in rent.
Compared to the rest of the Seattle Metropolitan Area market, the Tukwila submarket has lower rates, so you should have no trouble finding a great deal in this undervalued region.
In the last 90 days, 5 listings have been listed, which means new availabilities 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 posted, so finding a space for a small business might be tough.
Even though the median size is 16,630 sqft, there are still 0 office spaces below 2,000 sqft. Most properties in this region are around 2 floors. Most buildings in this area were built in 1979 and are Class A.