Thank you those that have posted generally useful comments so far. I would respond as follows:
The effectiveness of a potion/item depends upon the skill of the maker - if herbs were to be similarly affected i. e. the herb had less effect/the effect lasted less time/the herb could be stored in pouch less time all these things affected by the pickers skill level then I am sure we would soon see differential pricing of herbs.
I do not agree that time taken to produce the potion/item should be a factor a Loremaster chooses his profession and learns his skills in making things to improve the quality of his goods progressing to being counted an artisan maker of goods to the highest mortal standards - this is the investment of time that affects the pricing not the 5 seconds it takes to mix a potion.
However if anything I would agree with Korinal, certain herbs maybe are underpriced although Teylos gives useful innersight into how herb pickers price their wares.
I can assure you if you keep see the pressure and demands on Loremasters to provide their services you would see it's not just a case of a quick couple minutes to mix someone a potion or charge an item it an sometimes be a BIG hassle.
To Shriek, point taken re lastagii but of course any decent player would take Lestagii and a Potion at the same time surely.