If you want to save on downtown parking costs, consider parking your car outside of downtown and taking the free downtown buses.  Metro buses are free in the downtown area between 6 a.m. and 7 p.m.  The Ride Free Area extends from the north at Battery St. to S. Jackson St. on the south, and east at 6th Avenue to the waterfront on the west.  The bus driver will announce the last free stop when leaving downtown.

If you look hard, there is some free parking near the Space Needle on the north side and SAFECO Field on the south side. From either of these places, you can access the free zone bus system with not too far of a walk (or just by taking the monorail from the Space Needle). Just be sure to pay attention to the street signs when you park, and also be watchful if walking in the SAFECO area after dark.

Information about the Ride Free Area (including a map) is available at the King County Metro Transit website.