Commensurate means proportionate, not equivalent. A $100 reward for rescuing a $100 billion ship is not commensurate, and neither is a $100 billion reward.
Well then what's the factor? 0.1? 0.5? 0.7?
From what I recall, its 25%
Oh it gets better, they could declare General Average https://en.wikipedia.org/wiki/General_average and then instead of buying new one of what you lost you are chipping in for everyone else on board.
If that was the deal, forget salvaging it, just buy a new one with the cash instead.
Just ditch the ship and buy a new one if that's the choice you face.