an arm and a leg vs silly money

an arm and a leg

noun
  • Usually used after the verb cost, but also often charge, pay, and spend: a very high price for an item or service; an exorbitant price 

silly money

noun
  • A ridiculously large (or, less commonly, small) sum of money. 

How often have the words an arm and a leg and silly money occurred in a corpus of books? (source: Google Ngram Viewer )