I didnt know you can get discount on potions.

Damn ... still there are undiscovered things. :3
You can get a discount on buying and better prices on selling by giving vendors gold. Its expensive though, about 1,200 Gold or so to get their approval up to 100%. In the case of Ethel its very much worth it because she makes the best potions in EA and has 3 x Elixir's of Hill Giant Strength per long rest.
Elixirs of Hill Giant Strength now last until long rest. This is HUGE. I now build characters around the idea of just popping one after every long rest.