Most of the limo services, e.g.
http://seattleexclusivelimo.com/ - will charge $50 - $60 from Bellevue to the airport. Eastsideforhire uses a lot of Priuses, which obviously won't work for your party. The limo companies mostly use Lincoln towncars which are big enough, as long as somebody doesn't mind riding in front. A metered taxi will be a lot more.