If it is made by robots, so it is completely a commodity, then its cost can be equated to energy.

However, most things take someone's time, energy and know-how. Even if that person is using machinery that is practically free.

And artisans pieces take even more time and skill.

Food is an interesting example. We factory farm food right now, so it is conceivable that it could become completely automated. However, this is not the case. We will find that no human energy input equals no human consumable food output.

Human energy input will be vital, even with free energy, electrical sources.

And, keeping track is now being done by computers and block-chain. That is the place where the free energy really makes it free.

Until humanity gets to such a stage where everyone naturally feels like pulling their own weight, then we have to continue accounting for our personal energy.