Probably five-fifteen thousand, if you're planning to take a vacation there. I don't really think you'll go there, step a foot down, say "Well, now I'm done. Time to go!" and go back into the plane. Maybe a thousand give or take for the plane.
It's less if you're only going to go backpacking there, but I doubt you really want to go to Japan because of the land. Remember, Japan is pretty expensive, and you need to EAT while you're there, as while as pay for a room, pay for trains and transportation, shopping, tours, things like camera batteries or film, gifts, and whatever else you can tack onto a vacation.
And to live there? Don't even ask.
