Cheap accommodation for one person

Airbnb shared rooms or CouchSurfing would probably work for you. Taking a Bolt Bus between cities is probably the cheapest option for transportation. It only cost me $17 to go from Portland, OR to Seattle, WA vs $50 via train. Although I heard taking the train is more scenic, as long as you sit on the right side of it. My first trip to Portland was only 3 days and I felt like I got a pretty good grasp of the city and culture but Seattle has way more to do. Maybe 5 days should get you pretty acquainted? Stay in Capitol Hill Neighborhood if you can and buy a City Pass for the all museums and stuff!

Hawthorne Youth Hostel http://www.portlandhostel.org

Definitely check out Airbnb - if you filter by shared room or private room, there should be a few listings within your budget, and you have the added bonus of staying with a local! 

Hi Tienzai,

I moved to Seattle about 8 months ago, and work in the tourism industry up here, which has taught me a lot about the city! Some places that could be cheap options:
1) Green Tortoise Hostel Seattle(around $30 a night). This hostel is literally right in the middle of downtown, right across the street from Pike Place Market (one of the best attractions in the city)
2) Couchsurfing. If you make an account with Couchsurfing, you can find people who will let you stay at their house. I've done this before, and genuinely you can make some great friends this way, and usually you will get to spend the night for free. You get to choose who you stay with too, so that way you won't end up sleeping over at a creepy person's house.
3) Look up hostels and hotels in the South Lake Union/ Northgate Neighborhood area of Seattle. Those areas tend to offer cheaper accommodations then downtown hotels :)

I would recommend 2 or 3 days to stay in Seattle, also! Check out Pike Place Market (the oldest and largest outdoor market in the US), walk along the waterfront, take the Seattle Center Station - Seattle Center Monorail, and check out the Seattle Center. If you want a good view of Seattle, go to the Columbia Center Sky View Observatory. It is the tallest building on the west coast, and you get a 360 degree view of Seattle. It's cheaper than going to the top of the Space Needle also! And if you like seeing the attractions in a city, look into getting a City Pass. It gets you into all of the major museums, zoos, and city cruises for cheaper.

Enjoy your travels!

-Ketti

For such low cost accommodation I would check out couchsurfing.org, airb&b, and there are even hostels available. 

Try a roomshare? something like airbnb.com you can probably find a private/shared room -- or also could search for Seattle Hostels, might be something there --
hipmunk.com is also a good tool

Portland has some great hostels. I would check them out.