Dime a Dozen

Etymology:

• The U.S. Continental Congress officially announced the ten-cent coin a "dime” in 1786. It became a famous coin that almost everyone had because it was very cheap and easy to get. So this expression became common to refer anything that was easy to access. To make this expression catchy, the word ‘dozen’ was used with ‘dime’ as both begin with the same letter ‘D’.