The process of getting a visa in any Southeast Asian country is usually simple, but the kind of visa you apply for, the duration of stay you get, the ability to have multiple entry and the costs can vary.
The most sophisticated program is Malaysia’s MM2H but although it has great benefits (10 year renewable being a big one) it does require a $50,000 deposit be maintained for people over 50 years of age.
Thailand requires less than half that amount but it must be renewed annually.
The Philippines cost falls in between but does allow you to work in country while the others do not and has no end date.
Cambodia and Vietnam don’t have retirement visa programs as developed as these three requiring constant renewals and some fears about changes in government policies that could well occur.
In almost all cases foreign sourced income is not taxed while income earned in country is. The question you have to answer is this: do you want permanent residency or an ongoing ability to come and go as you please? You may only want to spend six months in country every year, but if you intend to return every year then permanent residency is better than going through an annual application process in our view. And, once you have that, you really can come and go as you please. Keep in mind, a longer-term visa is only granted for as long as your current passport is in effect. You will not have to re-apply, but you will need to get a new visa or stamp.