I don't see where the money is going to come from. GM stock has been basically flat ever since they went public again, GM is exiting the car business because they are not competitive, I am seeing adds for $12,000 off on their new trucks, GM's self-driving car business seems to have flopped, they have basically failed in electric cars and the only thing that I have seen advertised other than discounts is a nifty tailgate. When you add in that by historical standards we are already overdue for a recession in general and the auto business in particular things aren't looking good for GM. I sold my stock in GM several months ago.
As for the amount the negotiations themselves, if all of the UAW workers in my area quit I believe that GM could get qualified replacements as fast as they could process the paperwork for at least a 30% discount. Then GM would have a fighting chance in the market. I dare the UAW to test that theory.