I don't know the answer precisely, but I had this conversation with an elder once. The elder admitted that the cost of printing a magazine was pennies, he said probably a nickel or less.
So, I reminded him that the "brother" on the platform told us that when donating for publications, we should compare our book or magazine to what a similar book or magazine sells for at Barnes and Noble or some such bookstore, and donate accordingly.
I also reminded him that the WT does not have the operating costs that commercial book publishers have. WT does not pay their "employees", they do not pay their writers, they do not pay for advertising, they do not pay for the gasoline that their "sales people" use to go door-to-door, they do not spend towards a clothing allowance, and they most definitely do not pay TAXES!
So I asked him why should a JW pay a comparable price for WT literature that they would pay for a commercial book or mag?
Needless to say this elder does not speak to me anymore!
As for what each Watchtower magazine is worth? (This is too easy) It isn't worth the paper that it is printed on!