Use dropdown options for calculation?

Hi! Love the plugin, its just what I needed! But a quick question.
The form i’m building is for an event registration. Using the GF Lists and your dropdown as one of the columns, I need to get a yes/no option for if the registrant wants lunch (costs $).
So what i wanted to do is make a dropdown for ‘lunch’ with yes/no. The problem is I can’t make that into a calculation. If its a 0/1 then I can make the ‘1’ into a calculation, but do you know a way to use yes/no as a calculation?

Does that make sense?

Thanks!