These were not isolated, cut-off-from-humanity backwoodsmen, and it would be simplistic to suggest that only the mountaineers engaged in "subsistence plus" agriculture. They sold surplus agricultural products to distant purchasers, so their farming was "subsistence plus" - not purely for local survival, but not primarily for cash either.
Of course, the Todewater Virginia area, with all of its river-based transportation, still included a lot of self-sufficiency in producing food and clothing on the plantation for local use. Storekeepers had to extend credit and engage in barter for three centuries, until network of paved roads was after completed World War Two in some areas. Today the economy revolves around cash throughout all regions of Virginia - but some Floyd County residents are using a local form of "script" rather than Uncle Sam's greenbacks, to assist in the purchase of local goods. The homogenization that comes with the arrival of a Wal-Mart may be on the horizon, but local pride and boosterism is still alive in Floyd.