Totally depends on what area of Seattle or King County you are looking for and what you need. Closer to downtown Seattle or Redmond, the higher the price. You can get a look at prices by going to the website of Dupree and Scott. They are a large company that tracks the rental market.
In the Renton area where I work, the rental price has gone up 10 to 15 % since last summer. I know of a couple condos that are currently for rent. If you need further info, please call.