I need a breakdown of the item costs:
Base price Mithral +1 Enchantment
I’ve read that there have been conflicting prices between the Core Rulebook and Ultimate Equipment.
I checked both the Core Rulebook (6th printing, 2013), Ultimate Equipment (2nd printing, 2012), as well as the Pathfinder d20 SRD. All of them have the same information about arms and armor made of mithral. I've quoted the relevant parts below:
Spell failure chances for armors and shields made from mithral are decreased by 10%, maximum Dexterity bonuses are increased by 2, and armor check penalties are decreased by 3 (to a minimum of 0).
An item made from mithral weighs half as much as the same item made from other metals.
Weapons and armors fashioned from mithral are always masterwork items as well; the masterwork cost is included in the prices given below.
Shield +1,000 gp
Calculating the price and stats:
First we start with the 20gp base cost of a heavy steel shield, because it's metal like mithral. Then we add the mithral cost of +1000gp, which means it already counts as masterwork. Finally, the shield gets a +1 enhancement bonus that increases its price by another +1000gp.
The total price is 2020gp. The shield weighs 7.5 lb for a medium-sized creature, or 3.75 lb for a small-sized creature. It has an armor check penalty of -0, and a 5% arcane spell failure chance.