Most listings are in the $30's per square foot per year. The Mercer Island submarket is going through a decrease in rates. In the last 3 months, the median rate fell $6 per sqft per year. That's a 15% decline in rent.
Compared to the rest of the Seattle Metropolitan Area market, the Mercer Island region has higher rates, and you'll need to pay a premium to be in this hot region.
In the last 90 days, 1 listings have come on the market, which means office spaces 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 980 sqft. Most buildings in this region are around 2 floors. Most buildings in this region were built in 1982 and are Class B.