I think stating the salary range and then providing examples of the CoL in the area without trying to justify the salary range in comparison to it is the best way to advertise the position.
Saying what you just said: We are looking for great candidates wanting to live in beautiful southern Idaho is compelling too (for people wanting to get away from the huge and congested cities).
Anyway, random internet stranger conversations, take it all with a grain of salt :)
And yes, we also get a lot of people (myself included) who are escaping from California for various reasons. Considering the number of people who leave California, it's almost surprising that California's population is still growing, though I believe it is.