On average, listings lease in the $30's per square foot per year. The Mercer Island region is experiencing a decline 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 greater rates, and you'll have to negotiate above asking rent to be in this hot region.
In the last 90 days, 1 listings have come on the market, which means new listings are probably leasing quickly. You'll want to be prepared to make an offer immediately. 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 980 sqft. Most properties in this area are approximately 2 stories. Most buildings in this region were built in 1982 and are Class B.