pretty penny, a

1. A considerable sum of money, as in That fur coat must have cost a pretty penny. [Early 1700s]

Example Sentences

And if he had spoken to me on the subject I might have saved him a pretty penny—a precious deal more than the paltry sum which he and I had a quarrel about at that time—a matter of business, sir—a pecuniary difference about a small three months' thing which caused a temporary estrangement between us.

From Project Gutenberg