And time of the operator is $0 per hour as well
The fact that the analysis can be carried out in monetary units (because we don't have a good direct measure of utility) doesn't mean that receiving money itself is the only source of utility that needs to be considered.
The commericial overhead rate for an SLA printer is about $5 a plate - the washing and curing steps can be largely automated, or even if they are done manually, it's not that much work.