Arkham horror and Game of Thrones have bigger boards, but you're not likely to find them cheap.
Wow. What a perfect answer. I dug out my copy of Risk (it was in the garage, of all places) and sure enough, that one should do the trick.
Thanks, Reefgator. I'd tip you, but I have nothing to share but the song in my heart.
Unfortunately, that song is a polka ditty that has been lodged there for days.
EDIT: My ship came in! Thanks for the funds, Puquak.