If someone decided to check Han Yu's purchases, he would appear like a hardworking alchemist dedicated to the local method. He bought the materials, so no one suspected him of using the cheap, abundant, familiar Great Continent recipe.
In reality, all those expensive herbs went straight into storage. He used almost none of them.
The only herbs he consumed were the cheap ones. And they were plentiful. Nobody cared about them. Nobody competed for them. Nobody even bothered bidding for them in bulk.
The Blood Gooseberries grew like weeds in several tributary valleys. The Blood Thorn Nettles were literally considered invasive. The Spirit Fenugreek Seeds were imported occasionally from nearby regions but were common enough to never spike in price.
Because nobody else had thought of the Great Continent recipe. Han Yu was the only one. And so his production cost remained laughably low, while the selling price continued to grow. He also diversified his selling methods.
