who will also continue to make profit on the labor the lower class does to afford anything above basic necessities
If someone can afford basic necessities, they aren't going to choose to work three jobs at minimum wage where they are treated badly, forcing an improvement in pay/conditions to find any workers. As for setting prices arbitrarily, that isn't actually possible except where a monopoly is held, the idea that supply and demand influences price is not a myth. Having money and the choice of how to spend it does actually give you additional agency and leverage, and UBI would serve as a form of redistribution if it is funded by taxes of some kind.