On cazic thule, I think the average price is about 80pp, but for instance, right now i can buy it in the bazaar for 70. With a low trivial like this potion has, a lot of people make it at any time, and they fight for the customers, which consistantly drives the price down until a lot of shammys won't make it anymore because its not profitable enough. At that point the price raises again, because there are less people making them, so less competition to undercut the price. it's just supply / damand.
its a vicious cycle, but the trend should apply to virtually all servers over a long enough period of time.