What does a dime a dozen mean?

Question

a deeper meaning not just 10 cents for 12

Answer 1

it means something is very common.  Back in the day that was the going rate for a dozen, I guess (probably donuts)

Answer 2

It means that 12 of something costs ten cents.

Answer 3

It means very cheap. "10c for 12 of something" would be the literal meaning...but as a figure of speech it just means cheap.

Answer 4

It means that whatever it is, is very common, and that you need to get something more unusual.

Answer 5

It means that the subject of the phrase is something that is very common and not rare or unique at all.  Running backs in the NFL come a dime a dozen nowadays.