Most listings are in the $20's per square foot per year. The Burien region is experiencing a a boost in rates. In the last 3 months, the median rate increased $21 per sqft per year.
Compared to the rest of the Seattle Metropolitan Area market, the Burien region has less expensive rates, so you should have no trouble finding a great deal in this undervalued region.
In the last 90 days, 2 listings have been posted online, which means new availabilities are probably going fast. You'll want to be prepared to tour spaces as quick as possible. About 250% of the office spaces in the Burien are subleases, so you might be able to snag a great spot on a short term. There aren't many listings below 2,000 square feet available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,280 sqft. Most properties in this region are approximately 2 stories. Most buildings in this market were built in 1979 and are Class B.