For starters your plane ticket will cost around $1000 for a round trip. It can cost more depending on what time of the year you plan to go. You may be able to find a cheaper flight if you look around.
As for spending money goes You may want to bring about $100 a day (though this is probably the least you can get by with. not including a hotel)
A hotel is about $100 (according to Expedia $98)
All together that would come out to about $2200 for a weeks stay in Japan. (Its a rough estimate so it could be more.)
I went as a Exchange visitor for 5 months for my stay in Japan last year and I spent over $3000 for everyday things like food and karaoke
(this is of course because I did not have to pay rent or for dinner meals.)
If you talking about living there, rent for a standard apartment could start as much as $500 a month but A more practical cost is $1000 a month being that it would be very hard to find a place that costs $500. Gas and electricity may not be included in the rent, and some these places don't even have there own running water and may have a joint bath room (for all the tenants to use) If they do not have a joint bathroom they my have a bath house near the apartment you would be living in. Bath houses cost about 100-200 yen about 1-2 dollars to use. Keep in mind that you are you would be a Foreigner in Japan and most Japanese (sorry to say) don't trust Gaijin in their apartment as most leave before there lease is up and/or do not leave the apartment the way it was before. Typically they have a larger down payment for Gaijin so your looking at something 1700 dollars a month.
Your best bet may be the Gaijin House that you may find around Japan if you plan on staying for a month or so. (I've never really seen one but I've heard that there out there) Cost is between $500 $1000 per month. This (supposably) includes a futon and maybe a Table possibly some kitchen utensil's (like I said I don't know Ive only heard of them)
I think thats about I'll I know for cost of living in Japan. I hope you found it useful and good luck if you plan on going to Japan
