I made a pretty big discovery at the supermarket today: E.L. Fudge Original (henceforth ELF-1) and E.L. Fudge Double Stuffed (ELF-2) sell for the same price at the supermarket. My first thought was that the fudge stuffing must be both free to produce and completely weightless. I quickly discovered that the ELF-1 package actually weighed more than the ELF-2 package, suggesting that the fudge was not weightless but rather some sort of anti-gravity substance that caused the package to weigh less.
It wasn’t until I got home, and opened and carefully examined my newly-purchased ELF-1 and ELF-2 packages, that I understood that there were actually more ELF-1 cookies in their package than ELF-2s in theirs. Assuming there is indeed twice as much fudge stuffing in an ELF-2* and that the shortbread portions of the cookie weigh the same in ELF-1 and ELF-2, some very basic linear algebra will show that rather than having negative weight, a unit of fudge stuffing weighs 1.42 grams.
As far as the the price of producing the fudge stuffing: given the equality of the prices of the packages, my calculation is that the elves can produce 2 units of fudge per single piece of shortbread (there are two shortbread pieces per cookie). Of course, that is only if the price is supply-driven. More likely, it is demand-driven: if the prices ELF-1 and ELF-2 diverged, demand for whichever was cheaper would increase so heavily that it would preclude the feasibility of producing both versions.
The other fascinating bit of data in the above table: the number of calories in an ELF-1 is the same as in an ELF-2. I don’t know enough about food to make any sense of this, but it might be evidence that the shortbread portions of ELF-1 and ELF-2 are actually different. Otherwise the fudge would have to be calorie-less while still contributing fat.
*Allison has done some (methodologically questionable) research on the related question of “Is there twice as much stuffing in Double Stuf Oreo than in a regular Oreo?" and concluded there was not.