Yeah, it's generally cheaper to live in certain countries, like Mexico, but AFAIK, there are plenty of places in the US with similar property values to tourist-friendly cities in Mexico. I know a lot, because I'm looking to buy a place in Mexico and Cabo is high on my list (as I'm from Southern California, I find the scenery of Baja California very familiar). So is Puerto Vallarta, which is less known, but similarly priced (and verrry popular with ex-pats).
The biggest difference is, IMO, the weather in touristy parts of Mexico is generally nicer than the weather in places in the US with 150-200k homes (though the summers are quite hot). Other counties are cheaper, no doubt, but I'm not sure it's as cheap as some people think (at least compared to living in a very low coast of living rural part of the US).
(I'm looking for a winter home, bc, prices in Southern California being what they are, it's significantly cheaper for me to own a home in the PNW and in Mexico than to buy one anywhere near where I grew up in Southern California).
I do think, generally, the WWM survey shows more books = more money, but it's not as linear as people would hope. We can't just push out books and expect more money. It's more that people who stick around, and keep writing more books, are the ones who start making money.
I have 30-something books and I don't really see my backlist income grow, overall, when I add new books. With visibility from a new release, sure, but not from the book itself. I think most readers are only going to read 3-5 of our books, with another segment reading 5-10, so beyond a certain point (I'd say around three finished series), additional books/series start to see diminishing returns. People have limited attention. Authors too. We can't promise ten series, all the time, with equal results. If I put two free books in an email, I'll see fewer attention to each book than if I put one, etc.