A logistics suggestion from someone who tries to get out west every year and ships his bike: Are you going to be spending the night somewhere in Seattle? If so, you might want to consider looking for a shop that is close to where you will be staying rather than one close to where you will be landing. Seattle has a nice HI hostel in the thick of the city. It's close to the Bainbridge and Bremerton ferries. When I did ACA's group Northern Tier tour we met in Seattle, stayed at the hostel's old location and then caught the ferry to start the tour. I went out a few days early so I could have a full day in the city to see the sights and relax.
Also, the hostel is about 2.0 miles from the Seattle REI. Some REI stores will receive and assemble bikes for people who are about to start tours. Two years ago I used the Missoula REI for that very purpose for a tour starting in mid-June, and I will be using them again this June. They only charged me $40 to re-assemble and tune the bike, which is very reasonable. It's also handy because you can pick up any last minute items you might need, like fuel for you stove. You would have to call the Seattle store directly to see if it offers the same service. REI's extended hours are also helpful, especially if you plan to start a tour the day after you land. I landed in Missoula some 4 hrs. late. Had I used a LBS in town, I would not have made it there before the shop closed. REI, on the other hand, is located right next to the KOA where I started the tour and was open until 9 p.m.
If you decide to go that route, I would call sooner than later and get on the schedule. The Missoula REI wanted to have the bike in their hands at least 10 days before my arrival because it gets very busy around that time. I would also make hostel reservations early. When I stayed there in late May of '99 and '00 the place filled up. They are in a different location now, so it may be larger, but I wouldn't chance it.
Finally, I highly recommend using bikeflights.com to ship your bike. They are basically a FedEx discount shipping service for bikes. I have used them twice with excellent results. Their web site has a handy calculator that will provide you with a quote. All you need are the origin and destination zip codes, box dimensions and total weight (which you can always estimate). Last year I shipped my bike from Philly to Rapid City, SD. At an estimated weight of 60 lbs. for the bike, box, racks fuel bottle and stove, I paid $47 each way including $1,400 in insurance and a $5 surcharge for pick up at a LBS (as opposed to taking it to a FedEx shipping place, such as a FedEx-Kinko's store). I believe that included a 10% discount for being a repeat customer. Still, that's hard to beat for four-day shipping.