1
general::
Phrase(s): a dime a dozen
Fig. abundant; cheap and common. • People who can write good books are not a dime a dozen. • Romantic movies are a dime a dozen.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
So plentiful as to be valueless. For example, Don't bother to buy one of these? they're a dime a dozen. The dime was declared the American ten-cent coin in 1786 by the Continental Congress. [First half of 1900s]
American Heritage Idioms