On average, listings lease in the $20's per square foot per year. The Burien region is going through a a rise 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 lower rates, so you should have no trouble finding a great deal in this discounted submarket.
In the last 90 days, 2 listings have been listed, which means spaces might be leasing quickly. You'll want to be prepared to make an offer immediately. About 250% of the available leases in the Burien are subleases, so you might be able to find a shorter term or below market rent. 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 1,280 sqft. Most buildings in this area are approximately 2 floors. Most buildings in this market were built in 1979 and are Class B.