Seishun 18 kippu (青春18切符） 2007-2008 Winter
The Japan Railways Group has just announced a Seishun 18 Kippu special for the upcoming Winter 2007-2008 season. The special-deal Seishun 18 Kippu will be offered at 11,500yen, five (5) days of unlimited travel on any JR futsu (regular) and kaisoku (rapid) trains along with a very small number of exceptions permitting travels on express trains (e.g., between Kanita and Kikonai sandwiching the Seikan Undersea Tunnel).
For the Winter season, you can buy the Seishun 18 Kippu between 1st December 2007 and 10th January 2008, and the pass can be used between 10th December 2007 and 20th January 2008 (last day of travel with Seishun 18 Kippu).
This is about the cheapest way to travel for five days in Japan that I have ever heard of, short of hitchhiking and/or walking. Granted that it can be tiring to travel far on a futsu or even a rapid train, but at only 2,300 yen per day, you don't even have to go the distance to make it worthwhile.
