1
general::
Ruin one financially, exhaust one's resources, as in I guess the price of a movie won't break the bank. This term originated in gambling, where it means that a player has won more than the banker (the house) can pay. It Also may be used ironically, as above. [c. 1600]
American Heritage Idioms
2
general::
Phrase(s): break the bank
Fig. to use up all one’s money. (Alludes to casino gambling, in the rare event when a gambler wins more money than the house has on hand.) • It will hardly break the bank if we go out to dinner just once. • Buying a new dress at a discount price won’t break the bank.
McGrawhill's American Idioms And Phrasal Verbs