Tricky business though, as many lower cost-of-living areas also have lower wages, and fewer job opportunities.
I sold off part of my grandfather's farm in rural Ohio a few years ago - the house and a few acres - for an incredibly low price. However, within a sane drive from the spot, there were very very few jobs available, so that depressed the price methinks. A 30-year mortgage to buy the property would have produced payments of ~$250/month for principle/interest. That doesn't sound like much, but, where would that income come from?