You seem to be conveniently ignoring the 5 other apple sellers in you hypothetical town, all who will gladly undercut your business. Or the fact that everyone in town now has a basic income, so starting a competing apple selling business is much less riskier, as they have the BI to fall back on if their venture fails.
More demand can raise prices, that is fair. But implementing a BI does not necessarily mean that we are getting rid of capitalism, a system that tends to keep the costs of goods close to the cost of production. Also, it's worth noting that BI would most likely replace current welfare systems, so the 'net' amount of money that is put back into the system would be smaller than you are probably expecting.
More demand can raise prices, that is fair. But implementing a BI does not necessarily mean that we are getting rid of capitalism, a system that tends to keep the costs of goods close to the cost of production. Also, it's worth noting that BI would most likely replace current welfare systems, so the 'net' amount of money that is put back into the system would be smaller than you are probably expecting.