Chances of arguing or negotiating a reduction with them, is pretty much zero. And as soon as you hand in your notice they'll cancel your exit permit.
So I'd say your stark choices are either jump ship without giving notice, or pay the full amount, or expect to stay in Doha until you can pay.
Ask around the crew room for the story of the Panamanian F/O from a couple years back who was trapped in Doha for over a year with no job / no money / no exit permit. AAB is not renowned for being merciful
