According to http://db.vanillagaming.org/
You can't get the quest for the lung juice cocktail until level 45. http://db.vanillagaming.org/?quest=2584
You can't do the turn in of the librams unless you're 55. http://db.vanillagaming.org/?quest=4481
I can't remember but I think you have to have done the Felwood pre-quests to be able to loot the cleansed plants. If not, it seems to me, you had to be a certain level to be able to loot them. You would not be able to cleanse them anyway until you're late 40s.
A libram of constitution is about 30g, the turn in is 30g, to do the side quests, all the travelling, etc., 20g isn't an unfair fee.