Most "best places to retire" lists recycle the same handful of well-known destinations — which is exactly why they've gotten more expensive over time. The better opportunities tend to be the places that haven't shown up on those lists yet: strong healthcare access, low cost of living, a real community, and none of the price inflation that comes with being "discovered."
What actually makes a location an underrated haven for a fixed retirement income usually comes down to a few concrete things: housing costs well below the national median, favorable tax treatment of retirement and disability income, proximity to quality healthcare (VA or civilian), and a pace of life that fits what you actually want out of this stage — not what a magazine list assumes you want.
That's the same lens worth applying whether you're looking overseas or right here in the U.S. — Central Arkansas is a domestic example worth a look: no state tax on military retirement pay, a full property tax exemption for qualifying disabled veterans, and housing costs well under the national average.