(n.) Devil's bargain, (alternatively) Devil's own bargain:
An extremely bad deal, with a terrible price to pay, which someone considers accepting because they can see no other way out of a truly horrible situation.
Let's hope their friends can think of some better idea!
He knew she was offering a Devil's bargain, but he would do anything to get the medicine for his wife.
"If you marry that man to put a roof over your children's head, you will be getting the Devil's own bargain, because he does not love them, and he never will."