To clarify, when i said it “would have been negligible” what I meant more precisely is that “doing voluntary unpaid labor does negligible harm (and probably actually confers benefits) to the volunteer, so I didn’t factor it into the cost estimate”. This is very different from the question of “how much would the cost change if the volunteers were to be paid”—which is a question that I do not know the answer to.
To clarify, when i said it “would have been negligible” what I meant more precisely is that “doing voluntary unpaid labor does negligible harm (and probably actually confers benefits) to the volunteer, so I didn’t factor it into the cost estimate”. This is very different from the question of “how much would the cost change if the volunteers were to be paid”—which is a question that I do not know the answer to.