$40k USD is a fine amount of live off of is you are living in Carbondale, IL. But less so Chicago.
It's a pretty decent way to live in Belize or Costa Rica. Good luck in the UK. Germany, probably not, but Czech Republic may well be fine.
It depends on where you want to live. One of the factors which makes a huge difference is how old you are - the older you are the better healthcare you're going to need. Some of those low cost destinations don't have that great of healthcare - but some do!
Indeed,but it's easy for a person to move around the globe these days. It's conceivable and even common for people to work their careers in a high cost part of the world and then retire in a low cost part. I.E. the entire state of Florida