The goal is near zero marginal cost. Solar energy is zero cost and water should be relatively low cost. Additional materials have some cost, but the machine should prefer low value materials when possible.
Actual zero cost is not really possible (though solar energy is zero marginal cost, yeah?), but the point is to go for the lowest marginal cost that is reasonably possible. This is in contrast to how I see things now, which is that we have lots of redundant costs and waste due to competition that could be eliminated with cooperation. Of course, competition can encourage more efficient use of resources so there is always a balance.
But we don’t organize society for near zero cost now. Take driving a car to work. Not zero cost, but we consider it a worthwhile cost to perpetuate the system of wage labor. If everyone could work from home, total cost of survival would go down due to the reduction in automobiles.
The point of reboot is to think about how we can lower costs, not about how to actually achieve zero cost.