Ammunition

Ammunition is priced by dividing the base cost by the quantity field to arrive at a base cost per unit, and then adding the extra price per unit into the additional cost field.

For instance, a magically enhanced +1 cold arrow should cost 42gp each. The base cost autopopulates at 1gp per arrow, so that if you set the quantity to 20, the base cost field will populate to 20gp. However, only 1 of that 20gp base cost applies to each arrow, so to make up the 42gp cost of each, you must set the additional cost field to 41.