pretty penny vs valuable

pretty penny

noun
  • A considerable amount of money; a high price or a high income. 

valuable

noun
  • A personal possession such as jewellery, of relatively great monetary value. 

adj
  • Having a great value. 

  • Estimable; deserving esteem. 

How often have the words pretty penny and valuable occurred in a corpus of books? (source: Google Ngram Viewer )