Idiom - A dime a dozen

A dime a dozen

The phrase a dime a dozen refers to something very common and plentiful. In effect it has become cheap or inexpensive.

A dime is ten cents in U.S. currency that is one tenth of a dollar, or ten cents. The dime was first minted in 1796. In the 1800s, many goods such as eggs or apples were advertised to cost a dime a dozen in the United States. A phrase that began as a way to tout good value for the money evolved into a phrase that means something nearly worthless by virtue of its commonness and easy availability. In 1930, we see the first printed used of the phrase a dime a dozen to mean something common and unremarkable, the meaning a dime a dozen still has today.

Souce: The Grammarist

https://www.youtube.com/watch?v=WIyKdJxLhMo