Most listings are in the $30's per square foot per year. The Burien submarket is going through a a boost in rates. In the last 3 months, the median rate went up $13 per sqft per year. That's a 70% rise in rent.
Compared to the rest of the Seattle Metropolitan Area market, the Burien region has more expensive rates, and you'll need to make a great offer to be in this hot region.
In the last 90 days, 2 listings have been made available, which means office spaces are probably going fast. You'll want to be prepared to tour spaces as quick as possible. 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 960 sqft. Most properties in this area are close to 2 stories. Most buildings in this region were built in 1980 and are Class B.