a king's ransom
*a king's ransom
Fig. a great deal of money. (To pay an amount as large as one might have to pay to get back a king held for ransom. *Typically: cost ~; pay ~; spend ~.)
I would like to buy a nice watch, but I don't want to pay a king's ransom for it.
It's a lovely house. I bet it cost a king's ransom.