King's ransom - Suppose you are a minister of your king's kingdom. However your king has been kidnapped, then you will need big sum of money, to get him out of the trouble. Taking this in mind, this idiom means a big sum of money, really a big sum, which carries the potential to catch the eyes of others.
1. I saw him throwing bundles of notes in his briefcase; it was like the King's ransom.
2. Don't carry money like the King's ransom, it can prove to be dangerous for life.
3. “Well I think this is the King's ransom, lets steal it off", said the thief.