It depends what you want to do. The average person will only stay in Japan for one week, and if you just stay in Tokyo, you won't need a rail pass, and therefore, your expenses are lessened. There are Inns where you can stay for about $60-$70/night, so all you need is food, flight/transportation and spending money.
$850-1,200 round-trip airfare (approximate from West Coast depending on season)
$400-$600 lodging (approximate)
$100-$150 local transportation* (approximate, including to and from airport)
$200-$300 food (approximate)
Total: $1,550+-$2250+ (approximate) for entire trip; not including spending money.
*The Japan Rail Pass is valid only on JR trains. It cannot be used on subways or any other non-JR train. Meanwhile, prepaid cards don't give you any discounts, but they make the process of taking trains easier, as you do not always need to buy a ticket before riding a train.
Suica and PASMO
Suica and PASMO are prepaid IC cards, that can be used interchangeably on most trains and buses in Greater Tokyo, including JR trains, subways and other non-JR trains.
Official Tokyo Metro website
http://www.tokyometro.jp/en/ticket/type ... index.html