I went looking for an answer. What I found was surprising. New BP shotshells were selling for more than $42/box of 25. This was at Buffalo Arms website.
At first I thought that that had to be the price for more than one box but I was not able to find any additional info.
I do not know where that leaves you with pricing. I am sure, however, that pricing that high (or even half that) would keep me out of the market.