Costco does custom wedding invitations now:
http://pal.einvite.com/dept/Wedding/id/1.5/
Do you want to have the wedding IN Seattle or somewhere in the greater Seattle area? The closer to Seattle, the more expensive it's likely to be. There are some great wedding locations in the surrounding areas. Some friends of mine from Bellevue got married up on the shore of the sound near a marina in Anacortes. There are tons of state parks and whatnot where a ceremony and reception could easily be done in one location on the cheap--Kayak Point County Park in Snohomish County comes to mind.
Just some thoughts.