It is not fair to say potion should cost anywhere near 54 of an equivalent herb or poison. It would be far more fair to charge for the time it takes to mix or pick and prepare such items. For example is takes about the same amount of time for a loremaster to mix a 50 sip potion as it does for other professions to pick and prepare a single herb or poison. Loremasters also don't have to go and find the herb or poison in the first place but can mix potions anywhere. Also it is often the same people that pick herbs and poisons that spend more time planting them so it is not unreasonable that they should charge for their time and effort planting and waiting for plant to grow.