Question

An idiom a penny is a lot of money if you haven't got one

Answer 1

The idiom "a penny is a lot of money if you haven't got one" means that to those people who have almost nothing  will be able to appreciate what they currently have even the smallest thing available. Hope this answers the question. Have a nice day.

Answer 2

An idiom is a figure of speech that means something completely different than what the words or phrase actually state.  For instance, “break a leg” means good luck.  What is meant by the saying “a penny is a lot of money if you haven’t got one” is that more value is always placed on what one doesn’t have.  For example, one will value water more if dying of thirst in the desert than one who has plenty of drinking water to spare.