Renting a car in Seattle is very expensive owing to all the supplemental taxes -- essentially, we make our visitors pay for public projects residents don't care to pay for themselves. So, sorry about that up front.

You will do a little better price-wise if you pick the car up in the city rather than at the airport.

Seattle is a compact city -- you can walk its length in half an hour tops -- and there is no need to rent a car to see the central museums, the waterfront, Pike Place Market, the Space Needle, the International District, attend a Mariners game, etc. You can ride the ferries across Elliott Bay to Bremerton or Bainbridge without a car. The Museum of Flight down at Boeing Field is a $15 cab ride, or there's a Metro bus.

If you want to get out of the city to the wineries on the Eastside, the Boeing factory tour in Everett, Twin Peaks sites in Snoqualmie, across the Sound to explore the peninsula, etc., you will need a car for that -- public transport outside the city is thin and erratic. But perhaps you can just rent a car for a day or two if desired.