Since you're from California as I am, for a 7-day trip figure it this way:
R.T. airfare $700-$1,000 (shop around)
$250 for JR Railpass (if you plan to go around Japan outside of Tokyo, if not, you won't need it)
$60/night lodging (ryokans; but you can find business hotels for around \5,000-\5,500/night)
$15-$20/day for food
$100 for transport (taxis, trains and subways)
Whatever you want to spend on souvenirs/gifts