On average, listings lease in the $20's per square foot per year. The SeaTac region is going through a decline in rates. In the last 3 months, the median rate fell $1 per sqft per year. That's a 6% decline in rent.
Compared to the rest of the Seattle Metropolitan Area market, the SeaTac submarket has lower rates, so you should have no trouble finding a great deal in this discounted submarket.
In the last 90 days, 5 listings have come on the market, which means new availabilities might be going fast. You'll want to be prepared to make an offer immediately. About 100% of the available space in the SeaTac are subleases, so you might be able to sign a shorter term by taking over a previous lease. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
Even though the median size is 3,420 sqft, there are still 0 listings below 2,000 sqft. Most buildings in this region are around 3 stories. Most buildings in this area were built in 1979 and are Class B.