I don't think it comes down to cost imo (even for UG steroid products)
The fact is, when a label gets very big they will run into supply issues. They will not be able to import powders fast enough to meet the demand. They have 2 basic choices:
1- Lose money by being sold out of a certain product waiting for supplies to arrive.
2- Underdose products to increase their supply
It's really not about the cost of raw materials for the most part. A few raw materials are expensive (Tren, Anavar, primo, aromasin) Everything else is fairly cheap.