They aren't required by law to offer any amount of money, they aren't required to offer up enough money so there is no involuntary bumps. The normal procedure followed by all airlines is ask for volunteers and then choose names if they can't find volunteers.
It is not "normal procedure" to yank a passenger out of their seat and drag them off an airplane that he was already allowed to properly board.
They had already failed to follow any sort of "normal procedure", so the burden was on them to find a solution that did not involve violence against an innocent paying passenger.
I am, frankly, shocked that you would side with the corporation on this. I know that Loren and some of the others are authoritarians and always take the "might makes right" position, but I thought you held yourself out to be a Libertarian, and that the "free market" should be allowed to prevail.
A genuinely free market does not include using the violence of hired guns in place of "free market solutions".