Well, I apply this method since 2 game months now and I must say: it is genial !
I sunk the prices for grain to 90

in the moment, for timber it was some time down to 5

, but now I rise up to 45

and for beer it is 35

.
The storage cost´s are very high, so I sunk costs on one side and on the other side I made my population happy (so the number went up).
I was sceptically about the AI, if they ratten the system, but they don´t. The trick is simple. You have only to set down the prives in every town to the same level. So the AI has no market for selling and buying and they let the hands off it and trade with other goods.
Of course you have to produce the needed masses for this system.