Most listings are in the $20's per square foot per year. The SeaTac submarket is going through a decline in rates. In the last 3 months, the median rate fell $3 per sqft per year. That's a 13% decline in rent.
Compared to the rest of the Seattle Metropolitan Area market, the SeaTac region has lower rates, so you should have no trouble finding a great deal in this undervalued submarket.
In the last 90 days, 5 listings have been made available, which means 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 on the market, so finding a space for a small business might be tough.
Even though the median size is 3,420 sqft, there are still 0 spaces below 2,000 sqft. Most properties in this area are around 3 stories. Most buildings in this region were built in 1979 and are Class B.