Breaking The Bank

( spending more money than you have ... )

"Breaking the bank" is spending so much money that you have no money left. Example: "You really should not be buying this ring. You are breaking the bank."

"The bank" is where you keep the money you have, but the money you have is not enough after you "break the bank". Example: "If we tried to buy a house now, it would break the bank."

The thing which "broke the bank" is the thing you did after which you no longer have enough money to live. Example: "When John bought that motorcycle, it broke the bank. He had no money left for rent!"