cost a pretty penny

To be very expensive. The person spending the money can be stated between "cost" and "a." A fancy car like that costs a pretty penny, so I definitely can't afford it! Wow, a house in that gated community must have cost Alex a pretty penny.

Fig. to be expensive; to cost a lot of money. Mary's dress is real silk. It must have cost a pretty penny. Taking care of a fancy car like that can cost a pretty penny, let me tell you. It cost an arm and a leg, so I didn't buy it. A house that size with an ocean view must cost the earth!

Excessively expensive, exorbitant. The first phrase is American in origin and dates from the mid-twentieth century. The source is obvious: giving up an arm and a leg to buy something is clearly too costly. The use of “pretty” to mean considerable in amount was originally British and is now archaic except in a few well-worn phrases like this one, a cliché since the late nineteenth century. It was common throughout the eighteenth century, and crossed the Atlantic as well (“The captain might still make a pretty penny,” Bret Harte, Maruja, 1885). A similar term was a fine penny, now obsolete.