After the last session, a bunch of us were trying to figure out how much it would cost to make a certain scroll or potion. (As players most of us do not have unlimited access to the DMG, btw.) After looking at some snippets of the DMG that our DM produced we all became confused about what the "base cost" is and how it relates to how much we actually spend. As a group, we now feel that "base cost" is full retail price and that items can be manufactured for half of the base cost (+XP). (Although we never would have guessed that from the info we found in the PHB alone.) Is this correct?