If I were really looking for an 8-string guitar, I'd go for something electric first and a decent amp just to see if this is something I would want to explore.
http://www.musiciansfriend.com/guita...lectric-guitar
Oh, and I'd plan on keeping it too b/c I don't know anyone personally who's ever expressed interest in an 8-string, and I've known A LOT of guitar players in my time.