Possible Clues:

• Money earned producing off-the-peg garment
• Money earned available immediately
• Off the peg
• Not to order
• Prepared to put cheese back on the shelf for sale
• Of clothes, off the peg, not specially created
• Money earned exhibiting Duchamp's type of art
• Of standard shape or size
• It sounds as if the servant is prepared not to be bespoke
• Sort of money to be earned by Duchamp piece