From the archive
Taking an overnight bus in Japan
Night buses are a very cheap way of travel around Japan.
I will be the first to admit that my initial experience on an overnight bus was probably not under the most ideal circumstances. I had become sick a couple days prior to leaving, and while it was just a simple cold, the stuffy nose and lack of Nyquil were making the recovery a slow process.
Discussion
Depending on the company and level of service, you can have a range of prices for the same trip. Search well and book early for good prices and flexibility.
When I go somewhere I always forget to organize myself in terms of transportation. It's usually something I do when I need it, but your suggestion is quite good. And I actually really like travelling through bus :)