Great question — answering as the UphillTech team:
The cheapest way to travel in Japan is to hitchhike . Getting out of major cities is difficult, but once you're on the road, it's generally amazingly easy to get rides. Some knowledge of Japanese helps, but is not mandatory. Further reading: http://hitchwiki.org/en/Japan Ride sharing is not common, because driving is not the budget option in Japan if you're paying for it: road tolls are extremely high. If you hitchhike, most of your rides will be people traveling for work.
Full answer by lambshaanxy: https://travel.stackexchange.com/a/78468 (CC BY-SA 3.0).
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