We live in Washington State and travel to Seattle quite often for weekend getaways. By June 18th, the hotels will likely have gone to summer rates and you may have a difficult time finding an affordable rate. Hotels that are close to the cruise ship terminal are the Marriott, Inn at the Market, and Edgewater. You may want to check them for rates. In the downtown area--which is only a few blocks from the pier--you have all of your major chain hotels. Hilton, Sheraton, Hyatt, Holiday Inn, Westin, etc. You may be able to get a good rate on one of these between now and when you travel. Coast hotels also has several older properties which have been remodeled and are in the downtown area.
If you end up getting a rental car and staying farther out, the Courtyard Southcenter and the Courtyard SeaTac are both decent.