Generally speaking, the prices listed for ammunition for weapons are representative of general retail prices before the fall of Llael. More commonly, they will cost less.
This is because the Order of the Golden Crucible was based in Llael, and had a monopoly on the production of blasting powder used for ammunition. With the fall of Llael, the monopoly effectively ended, and even though the huge facilities the Golden Crucible owned fell under the control of the Khadoran Empire, hundreds of independent alchemists were now free to begin producing blasting powder without repercussions.
If a region has access to an enterprising alchemist with the ability to manufacture blasting powder, the prices in that region could be at least half as much as those listed.