extortionate vs worth a king's ransom

extortionate

adj
  • Of, related to, or typifying extortion (“the practice of obtaining money or other property by the use of force or threats”). 

  • Greatly exceeding what is moderate or reasonable; exorbitant. 

worth a king's ransom

How often have the words extortionate and worth a king's ransom occurred in a corpus of books? (source: Google Ngram Viewer )