We couldn't find any within walking distance to pier. We took cab from pier to Hertz downtown by Grand Hyatt. Hertz will reimbuse you $6.50 for cab fare. We picked up rental car downtown on return from cruise and returned at airport - no extra charge. Total charge with AAA for one day rental on Sunday after cab reimbursement cost about $33/day.
There are a number of car rental places in the downtown area. I have rented from Avis, National, and Alamo in downtown Seattle. The buses in the downtown core are free, so you can reach any of the rental agencies by free public transportation.