Note to the Nature of Wealth by John Ruskin

Cicero's distinction, "sordidi quaestus, quorum operae, non quorum artes emuntur", admirable in principle, is inaccurate in expression, because Cicero did not practically know how much operative dexterity is necessary in all the higher arts; but the cost of this dexterity is incalculable. Be it great or small, the "cost" of the mere authority and perfectness of touch in a hammerstroke of Donatello's, or a pencil touch of Correggio's, is inestimable by any ordinary arithmetic. (The best masters themselves usually estimate it at sums varying from two to three or four shillings a day, with wine or soup extra.)