Singapore Airlines for that kinda price? It's extremely cheap! I am interested, too. REALLY INTERESTED!
The only problem is, none of us speak Japanese, which could be a problem. And besides, the last time I went there, my transport and accomodation cost was like 7 times the airfare itself. It was a week trip in a motel with Japanese traditional paper divider in the room. And we took subways, shinkansens and buses wherever we go. Forget taxi, someone told me it cost like 250 Aussie dollars from the Airport to the Downtown!