I'm afraid you will find accomodations in the waterfront/pier/downtown area of Seattle to be quite expensive, though everyone's idea of 'reasonable' is different. My favorite waterfront hotel is the Edgewater, so you might want to check it out their site and see if it would be a possibility for you. Downtown, which is close by, are many of the standard chain hotels. There may be some smaller less expensive motels that I am not familiar with and hopefully someone who lives in Seattle will reply.
The best hotel, IMO, is the new Elliott Grand Hyatt. It was incredible in every way - the minute we drove up, they called us by name, knew how long we were staying, and pampered us like there was no tomorrow. But, the price was definitely more than what you'd pay at the Edgewater. We did get it for $200 off the regular rates with a AAA discount and then were upgraded to a corner suite $800 for free.
There's an Old Spaghetti Factory across from the Edgewater and it's a great place to get a delicious inexpensive Italian dinner before your cruise.