To say something costs a 'pretty penny' is to mean the item is
expensive
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This is just an imaginative way of saying that something is
expensive - it's not just worth a penny, the penny has to be pretty
on top of it!
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The cast of Pretty Penny - 2001 includes: Shane Luther as Chris
Kestie Morassi as Penny
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The phrase means that something is very expensive. The origin
comes from a gold penny that was minted in the 1200's that was
worth 20 silver pennies. Because it was gold, it was a pretty
penny, and if it cost a pretty penny, it was expensive indeed.