I'm going to be heading into the Mad Mage's pretty soon. Player wants to make a Gunslinger and I don't inherently see anything wrong with it. I know in Dragon Heist there is "Smokepowder", which is used with guns. I'm just trying to figure out a "sane" price for either crafting his own bullets/powder, as well as a cost to purchase them (tho purchasing will likely be in smaller quantities)

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Could anyone help a fellow DM discover the cost(s) to do said things without being too outrageous? I looked at the cost for arrows and bolts and its 1gp for 20 arrows. For sanity, I figured that would be fine, or do 2gp for 20 shots, or crating can be 1gp for 10 shots and takes a few days to formulate