First of all, the only way a non-permament resident/citizen can live here for as long as a year is to have a valid visa, either working or student.
Visa-providing jobs have a defacto minimum salary, because Immigration will not issue visas for employers that can't provide a living wage. This is generally about 200,000 yen/month, or a bit less if the employer covers housing and the like. 200,000 yen a month is not a lot, but it's certainly enough to live and train, and goes further the more frugal you are.
With student visas, the school that provides the visa should be able to tell you how much money you'll need for tuition and living expenses.
If you want to train here, you have to first decide how you're going to get over here, and then from there figure out how much money you need to save.
Josh Reyer
Swa sceal man don, žonne he ęt guše gengan ženceš longsumne lof, na ymb his lif cearaš. - The Beowulf Poet