Opportunity cost is the best alternative that is sacrificed for a chosen alternative.
(Layton, Robinson, Tucker, 2016, p. 33) The opportunity cost is classified as an option that is given up as best alternative and is therefore not where Bill spends $10 to buy the action figure. As opportunity cost is the best alternative sacrificed for a chosen alternative. So therefore, in this case the opportunity cost of buying the action figure is the Batman Graphic Novel because the graphic novel is the best alternative which is sacrificed and the action figure is a chosen alternative by Bill.
It cannot be an X Men T-Shirt because the graphic novel was Bill’s close second choice.