Normally, the coupon should be Buy A+2 free A+3, selling at $90. which is about $18 cheaper because A+3 is usually $118 in pharmacy.
For buy A+3 free A+4, the selling price is about $80 which is about $15 cheaper. For the selling price, it is from reading most of the postings here and I think that will be the market price which some mothers are willing to buy.
Also, some mothers think that the milk powders are more traceable if they buy coupons and redeem themselves, at least better than trading with some powders that they don't know where they are come from.