highway robbery vs unconscionable

highway robbery

noun
  • The act of robbing a traveler on a public road. 

  • Said of excessive or exorbitant prices. 

unconscionable

adj
  • Excessive, imprudent or unreasonable. 

  • Not conscionable; unscrupulous and lacking principles or conscience. 

How often have the words highway robbery and unconscionable occurred in a corpus of books? (source: Google Ngram Viewer )