Domestic? International?
What is the length of the proposed delay?
For domestic it usually is between $100 and $400. $100-$200 for 2+/- hours, $300-$400 for 4+/- hours or overnight. If overnight usually includes a hotel as well.
International is usually a little more as the length of delay is usually longer. I would expect between $400 and $600 for international.
I was offered $1k on the last international voluntary bump I offered.