Hopefully SEA rate can be extended for those just signing up! But if it can't, my recommendation is to check out
www.skyscanner.net (which is showing a lot of downtown properties at reasonable prices), or
www.kayak.com.
Obviously it's preferable to stay at the main hotel, but if it's now $200+, downtown SEA isn't that large that other properties wouldn't be easy walking distance. AFAIK it's safe to walk in downtown SEA or at least around the main hotels.
Remember: some chains require you to book through their websites to get points/stay credit, so keep that in mind when checking other portals. If rates are comparable, then going through your chain's website makes the most sense. If the rate is really cheap, you might be willing to give up points/stay credit. To each their own.
Cheers.