Source, in full
Reported in Bartlett's Familiar Quotations, 10th ed. (1919), stating "'All men have their price' is commonly ascribed to Walpole", and citing Coxe, Memoirs of Walpole, Vol. iv, p. 369: "Flowery oratory he despised. He ascribed to the interested views of themselves or their relatives the declarations of pretended patriots, of whom he said, 'All those men have their price'".