Alright guys. I've got a true shoestring dilemma here, for y'all. I have no plans for spring break and have roughly 9 days to spend doing whatever I want. Now, I live in Seattle and want to do some traveling, but I don't own a car and have literally no more than 300 bucks to spend. Maybe 400. But that's it. So... work your magic! Is there anything to do with that kind of money!

yep, you can get a cheap bus ticket to the next city over from you (pick one) and spend a few days exploring there. abracadabra.
Hitch hike down the coast (Hwy. 101) and back. Have you ever been to Depoe Bay, Oregon for example. The Whale Watching Capital (so they say) of the Oregon Coast. Get out a road map and look down the coast at all the little towns along the road.
Do some Googling for hostels on the coast. A dorm bed for under $20 is possible. So $180 for bed for 9 nights is doable if limited in where you will find you can stay. MickeyD's for 9 days at $10 a day is $90 and that's your $300 pretty much gone but doable. http://www.ocnsignal.com/oregon-hostels.html
A true challenge could be a true adventure. Adventure is defined basically as requiring the unknown and risk.