so I think after paying taxes and all I won't be able to save much.
this is quite confusing because different people reply with different perspectives.

my first year here was making 240,000y a month,

rent, for a small old ugly place, was 54,000y, and that's as cheap as you'll find it
I spent about 50,000y on food including going out now and then but mostly cooked
internet was free at the time, thank god for unsecured networks in crowded cities
phone was necessary and expensive, about 7,000y a month
I was sending about 100,000y back home a month to pay back loans

so yeah 300,000y is plenty if you know how to live cheap

now I make more than that but rent is about 130,000y, food is about 90,000y, utilities/phone/net 35,000y, and I'm saving a lot less than before towards getting a car

It's doable as long as you don't actually want to do all that much besides work and save. Go out for a few drinks and dinner on a regular basis and you'll struggle I reckon. I'm just about to turn 40 so doing everything on the cheap is well and truly in my past. Taxes aren't too much until after the first 12-18 months, then you have to start paying residents tax.

It is possible but it really depends on where you live and how you want to spend your nights and weekends.

I make that much and I usually can save about 140,000-150,000 every month. But I do not own a car and eat in nearly every weeknight and budget my spending on the weekend fairly strictly. And i rarely travel any further than an hour away from my house by train.

300,000 Yen is too much for me..
Usually they only give 220,000 Yen for starters..

which is the cheapest transport in Japan.
Is bus transport costly?

some of korean friends say that transport is costly there.

Using public transit supplemented with a bicycle is much cheaper than owning a car.

go for the moped or scooter for the cheapest, trains can get pretty expensive

if you're smart or lucky you work near where you live and just bike

3,00,000? 1,50,000?

I'm just hoping that they aren't hiring you for a finances related position. ;)

There used to be a decent net pay/tax calculator on jobdragon.com but it's now gone :( This one provides less details but also has some rough comparative data for other countries: MoneyToolshed.com round the world tax calculator

Move your mouse over the symbol and a more detailed breakdown and explanation will pop up.