I believe most (all?) registrars should let you give them a global DNS server, at which point your domain should be resolvable globally. Whether it’s reachable isn’t at the registration level, it’s at the DNS level. The blog author’s comment confuses me. Maybe they mean like having a TLD that matches each country with users? Seems not worth it.
You can get a domain for like $10 a year from many places. The national registrar I looked up was like $7 a year (Brazil).
Yeah, I think that’s right, but where your clients are is irrelevant. That’s what confused me about the author’s statement.