The short list right now is NW Arkansas, Kentucky, And Utah. But I'll tell him about Wyoming too.
NW Arkansas is gorgeous and friendly, but sales tax can creep up there in some locales. And avoid Eureka Springs like the plague. It's a very quaint, charming and historic town, but it has been a hub of LGBTQ degeneracy for decades now.
Instead, have him look a few miles to the north in SW MO - the Lampe and Blue Eye vicinity is nice. Lots of retired military live in the region - Table Rock Lake and Lake Taneycomo being the draw. Lampe and Blue Eye are far enough away from the tourist and resort crowds to make real estate more affordable too, and property taxes are still fairly low. Springfield is 50 miles north for commerce, better medical facilities, airport, etc.
We'd been looking at NW Arkansas cause a LOT of former Air Force said they retired there. Will relay SW MO as well