I just came back from an Alaskan cruise - which started and ended in Seattle. When I searched, the only hotel I found was Doubletree (located within minutes of the airport and about 20 minutes from the port). They offered airport and cruise ship transfers. They were a bit pricey but worth the extra money. Once we were there, we heard of other hotels offering the same thing. I believe there was a Comfort Inn and a few other chains right in the same area.
Enjoy your cruise. I loved it so much I am already starting to look into planning my next one!