Have you considered Vietnam?
VietNam
Interesting enough that I might give it a try sometime.
From what I read, you can get an apt there for $2-300/month and getting work is easy--common advice is that it's better to show up and look around. Pension would go a lot further than in Miyazaki. You can retain PR here, I think for up to a year (?), longer if you file paperwork saying you're going to be gone longer.
I've been to Oki several times. Low salaries, lots of competition (tho I never found it expensive). I guess your phone and health card would still work as expected, too.
(Whether you're aware, tho there is the US-Japan pension agreement, in the fine print it says that that does
not qualify you for Medicare--ouch!)