bargain basement vs megastore

bargain basement

noun
  • An area within a retail store, especially an area located below ground level, where the least costly merchandise can be found. 

  • Inexpensive. 

  • Of poor quality; of little or no value; low-end, shoddy. 

megastore

noun
  • A large supermarket or similar retail outlet; a superstore. 

How often have the words bargain basement and megastore occurred in a corpus of books? (source: Google Ngram Viewer )