As I have already said several times, the system is still being worked on and you are using an older version of the game. In V0.13, it takes 500 droplets for 1 potion and in V0.14, it decreases again to 250. And if this is still too high, there are skills to help with this and you can also go further into the cave to fight monsters that give more.
All the explanations are in the game, there is a book to explain the potions in the cave entrance and there are explanations about the skills in the PC in the hero's room. And if that's not enough, there's a GameFaq (the link is on the 1st page just below the 1st photo).