I don't have anything near that range, but you might take a look at the Cascade Bike Club rentals page. They list area shops with rentals - I'd call Aaron's, Montlake, Recycled Cycles, and Bike Station to see what they can do for you.
You might also post a similar message on the cascade message boards or at point83.com - another local club - a bit more boisterous than some :-)
http://www.cascade.org/Community/rental.cfm