The typical asking rate per listing is in the $30'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 rose $13 per sqft per year. That's a 70% increase 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 leases 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 available, 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 region are approximately 2 floors. Most buildings in this region were built in 1980 and are Class B.