When my dad was in college one of his friend's dad was called "Trader Lee" and he ran a trading post. He said he'd rather trade for something then sell it because people were often willing to trade something of higher value then they would spend in cash. For instance, you might buy a turquoise necklace for thirty dollars, but you'll trade a fifty dollar watch for it. When my dad knew him he had a building full of stuff that he traded and sold like that, hats, guns, jewelry, even cars out front. He was also a millionaire. If you're a crafty businessman, I think barter is viable in any economy. Though I think you start seeing it more the further you are from stores. Soldiers on deployment will trade back and forth. People on the edges of civilization have less use for cash and practically none for plastic.