> Will people who hear it hear the second or the first?
Definitely unambiguously the first unless they're the ones trying to "well acshually" it. At the point of the second you're not even talking about burgers - the maximum cheapness calories per dollar is a five gallon jug of corn syrup or something.
Can a particular fast food meal be cheaper than some similar grocery store meal? Yes.
Is a fast food meal cheaper that the maximum cheapness calories per dollar than everything you can get at a grocery store? No.
Will people who hear it hear the second or the first?