I am not sure about your situation, but most of the students I know here are either on scholarships or exchange program. I think that is your best bet for coming in Japan. Also, try to inquire in the Japanese embassy in your country about monbusho scholarship if available or get into the jica program. Students( undergrad ) under this program have an intensive one year japanese lesson, and they must pass level 1 or 2 ( i think ) after one year to be able to proceed.
If you get into this program, you will receive allowance from the govt of Japan. Though you are the one paying for apt., the govt will help you look for an affordable one.
So goodluck
