I have come accross the article where a gaijin living in Japan talks in detail about how much it costs to live there. He talks about rent, internet, health insurance, baby, etc, the picture is pretty complete.
Spoiler alert: according to the author it costs around 3035 EUR or 3313 USD per month to live in Tokushima, Japan.
It would be interesting to know if other people living in Japan agree with his estimations and anso how much the cost of living varies accross Japan.