A dime a dozen

Those are a dime a dozen. Cashiers are a dime a dozen.

This phrase is used to describe things that are cheap, plentiful, or easily obtained. It is a price. Perhaps it was once the price of donuts. Maybe you could get 12 donuts for a dime. Now it would cost more. Prices are sometimes worded this way. A dollar each. Five dollars a pair. But the idiom is "a dime a dozen", a dime for a dozen.

If you are choosing a career, you may find that your area has too many people in one profession, so their wages are driven down and they are less valued by employers. They are now a dime a dozen.

I don't want to be another programmer. Programmers are a dime a dozen these days.

Maybe someone could say that if their area is full of programmers and it seems like everyone is doing it, so they aren't paid as well as they once were, and companies consider them inexpensive and easy to hire.

Can I borrow one of these? You can keep it. They're a dime a dozen.

This means that the object is so cheap or inexpensive that the person is willing to give it away.

This idiom can also refer to things that have no price at all, particularly to people of a particular description, not just related to work.

Depending on the context, this idiom can be somewhat offensive, because it can sometimes imply that something is not only inexpensive or easy to obtain, but also that it is of little value.