[Nyororin]

I`ll just kind of ignore the number issue....

300,000 is alright. It just depends on what kind of life you want to live.
Decent apartment, frequent eating out, and a car in Tokyo... And you`ll be lucky to survive at all, let alone save.

Cheap apartment, transportation costs paid by the company with no car, mostly cooking at home, and living in a smaller city or suburb type area - you will probably be able to save at least 100,000/month.

A single person, living at the very minimum can get by on a bit less than 100,000/month. But that life would be nowhere near comfortable.

Either way, I would say ditch the car idea if you want to save.