dime a dozen, a

dime a dozen, a

Readily available, so cheap as to be without value. The dime being an American coin, declared the ten-cent piece by the Continental Congress in 1786 (the word comes from the French dime, for “tithe,” or one-tenth), this expression is obviously American in origin and probably owes its long life to alliterative appeal. Inflation has further degraded the meaning. Early in the twentieth century a dime could buy a paperback book (dime novel) or a cup of coffee and a doughnut; “Brother, can you spare a dime?” was the universal cry for a handout during the Great Depression of the 1930s.
See also: dime