The underdark healing potions being sold by Poromakh are sold cheaper than light healing potions can be crafted for. I'm not sure if this is intentional or not, but at 10 gp to craft and 9gp for magical potion bottles, light healing potions crafted by crafters are going to be significantly more expensive.
Poromakhs merchandise
Looks like these have been removed, so it seems this issue is resolved.