Have you downloaded and read through their school information?
Your fees will be (in yen):
Application fee 31,500
1st Year
Admission 52,500
Tuition 630,000
Materials 31,500
Facility Expenses 42,000
Total 756,000
2nd Year
Tuition 630,000
Materials 31,500
Facility Expenses 42,000
Total 703,500
It looks like you have to take 2 years minimum so you're looking at 1,491,000.00 JPY = $16,752.81 USD in school fees alone. This does not include your living expenses and lodging. You also need a financial guarantor who I also assume will also be your general guarantor (a Japanese resident). The forms also states that you need to submit a Purpose of Study document and that you and your guarantor be available for an interview prior to your acceptance.
This is a lot of money to invest on just a learning experience and not for career goals.
I'm sure other language schools or vocational institutes will have similar requirements and fees.
You might want to consider other options. Here's a website with some information although I don't know if it is up-to-date as some of the cost projections seem a bit conservative and some suggestions seem a bit overly optimistic:
Study Japanese Abroad in Japan