If you've never been to Seattle you have to see the Pike Place Market.
If you're watching money there are lots of places we visit frequently when we go there. The Fremont District and the Fremont Troll are popular spots that cost nothing but transportation to the place.
Another is the Hiram Chittenden Locks (good luck with my spelling there), mostly called the Ballard Locks. That's the place all the pleasure boats and fishing fleets for the most part get from the inner harbor to the sea. If you're lucky like I was once you can catch the Dangerous Catch guys heading for Dutch Harbor. Also a fine fish ladder viewing room.
Right down the road from there is Shilshole Bay Marina where you can see about any kind of boat you ever wondered about. The fuel dock there is where John Wayne used to tie up the Wild Goose when he visited for Sea Fair Week.
Follow on down that road to a great public beach where you will see anything from sun bathers to Kite Surfers. Then follow the road up the hill to see some of the best scenery out over the sound.
Kerry Park up Queen Anne Hill from downtown, http://www.yelp.com/biz/kerry-park-seattle
for the views you see in pictures and post cards advertising Seattle.
All those you can do without spending anything but gas.
Hope you have a great trip. We have kids in Seattle and have been visiting for years, love the place. If you want to stay downtown near the Stadiums visit the International District for some of the best food in the world. And if you do that find Uwagimaya's one of the most unique stores anywhere. Check out the rice cookers up in one corner from $9.00 to near $700. Again its a great place to just walk around and grocerys from around the world and a terrific food court representing many area of the world.