Free: Contests & Raffles.
I'm not sure I-90 would be any faster with the possible slow traffic you could get caught up in. Even with no traffic issues it wouldn't take much longer to go White Pass, and instead of taking 1701 over the ridge, take I-82, or the Canyon road, up to Ellensburg, and then into the Manastash. I would definitely avoid going through Olympia/Tacoma/Puyallup if possible.
The 1701 route is shorter but it ends up taking just as long as driving all the way around, staying on the pavement. Just depends on what you're in the mood for, a nice smooth ride, or a rough ride where you might see some animals.