a lot vs an arm and a leg

a lot

pron
  • A large amount. 

  • Many things, much. 

adv
  • Very much; a great deal; to a large extent. 

  • Often; frequently. 

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 

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