The Picture of Dorian Gray ch. 4 (1891). In Wilde's play LadyWindermere's Fan, act 3 (1892), Lord Darlington replies to the question "What is a cynic?": "A man who knows the price of everything and the value of nothing."
Oscar Wilde (1997). “Collected Works of Oscar Wilde: The Plays, the Poems, the Stories and the Essays Including De Profundis”, p.476, Wordsworth Editions