We'll always be able to find something which is still expensive. And everything has scaling limits. For example our "essentially unlimited" energy source migh

We'll always be able to find something which is still expensive. And everything has scaling limits. For example our "essentially unlimited" energy source might give us enough to power a 21st-century lifestyle essentially free, but might still be prohibitively expensive when you try to use it for intergalactic travel, or for running computer simulations of googols of universes.