I think you should let them decide the price. Have A set the price with
B having the option to buy or not. If B doesn’t want it, then A gets it and pays B half of the price. If B wants it, B gets it and pays A half of the price. The price should end up between 1- and 2- depending on whether both want it or don’t want it. Nobody should complain since the
decision was in their hands.