Hot dry state.
The cold states almost all use salt, even if they’re not very wet. (Though the wetter ones use more.) The exceptions are, AFAIK, Alaska and Colorado. However, you don’t want an Alaska car (seriously, if Carfax says that a car has spent more than 1 or 2 years in AK, cross that car off your list) because you have your choice of cars from coastal areas where salt spray is even worse than road salt, or you have areas where the roads suck (there goes your suspension) and it gets extremely cold in winter, meaning rapid temperature changes when starting are going to destroy your seals (or if you’re not careful, crack your head or block).
I don’t know how good or bad Colorado cars are…probably pretty good, though.
The sun in hot dry states tends to destroy paint, especially clear coat, especially on dark-colored cars. Reds fade really badly even if the clear coat isn’t destroyed. Rubber can dry out really badly, too. Dashboards crack on some models (early 90s Nissans, notably) really badly, too. Other than that, the conditions are ideal. You could strip all the paint off of a car in Arizona…all of it…and it would be years, maybe decades, before the rust became a structural issue. Hot climates are not a serious mechanical issue for most cars…they’re bad for the battery, but that’s about it.
Prices vary by type of car as much as by region. Also by season. A convertible is expensive in summer in a cold state, but expensive in winter in a hot one. A Subaru is cheaper in Arizona (where there’s little use for its abilities) than in upstate New York. Japanese economy cars retain a lot of value everywhere, but in Alaska it’s ridiculous (because they handle winter so well, mechanically…well, since the CV boots stopped sucking anyway).
Condition matters, too. In a salt state, a rusty car will be really cheap. A rust-free car will command a large premium.
The only reason to go outside your own town is if the local car market is really bad, though, and the only reason to go outside your state is if you’re looking for a specific car you can’t easily get there.