JETS, originally called monbukagaku scholars if memory serves, were on 300,000 per month and depending on the prefecture, some got subsidized housing, and some got free housing. In the mid nineties ( memory?? ) with the us dollar bottoming out at 86 yen, it was like probably a pretty good gig. The maximum number of renewals was for, for a total of five years and then they could become a CRT which is a kind of supervisor of Jets, International coordinator etc.
howver over the year MEXT cut funding and prefectures/school boards started outsourcing to private companies, such as interact. as well, over the years the sort of unspoken minimum salary of ¥250,000 per month to get a visa seems to have disappeared and outsourcing companies pay even less now. So this means that AET's, assistant English teachers, can you work for an outsourcing company for an unlimited number of years at a very low salary. no, with a very low yen and our first experiences with inflation and shrinkflation, it can be very tough for people who are making entry-level salaries that don't increase.
and it's an overcrowded market, and right now a buyers market (schools). So AET's are very tough situation.
Cheers