The story
A reference to peanuts (“especially of a salary: a very small or insufficient amount”) (originally US slang dating to the mid 20th century) and monkey (“a person of minimal intelligence, idiot”), with a humorous allusion to the fact that monkeys are fond of nuts.
First known use, by meaning
- from mid 20th c. Offering a low payment or salary will not attract skilled workers or employees.
Etymology from Wiktionary, CC BY-SA 4.0.