To use all or most of the available money or resources to do something: the website redesign break the bank
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with break the bank
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