Hmm... this could be an interesting discussion. So subsistence living does not require economies, besides some bartering. But most people wouldn't want to live that way, given the choice. Early economies came about due to marauders who would go from village to village pilfering. This was inefficient because it discouraged the villagers from generating any excess production for fear that it would be pilfered. Eventually villages began raising their own armies to protect themselves, and economies were created to feed and house those armies as well all the rest who weren't farmers, hunters, or builders.
So I guess I should correct my earlier statement to say that economies exist so that not everyone has to be a farmer, hunter, or a builder, and so that farmers, hunters, and builders can enjoy a standard living greater than that of mere subsistence.