No one armor piercing bullet, so there is no one cost. Most are inexpensive to make- less than $1 per bullet.
This all depends on your definition of armor and armor piercing.
There are several different technologies with armor-piercing bullets. A common one is for the bullet to have a thin core of steel, or other hard metal. Typically bullets have soft lead surrounded by soft copper. When these bullets hit something, they deform, usually increasing their diameter as they penetrate. Most armor exploits this property. Steel will not deform like lead & copper, and is much more likely to penetrate deeper than a regular bullet.
Theres Ball, Tracer, Armor Piercing Incendiary
It all depends on your definition of "armor" and "armor piercing".
An armor piercing capped ballistic cap is a variety of armor-piercing shell introduced in the 1930s.
Armor Piercing rounds, meaning, bullets go through more zombies the more it is upgraded.
You can buy armor piercing rounds for it, if you can find them.
Regardless of if it is legal or not, it is not ethical to do so. AP bullets are more likely to wound and maim, but not kill the deer.
An armor-piercing composite non-rigid is a variety of large solid projectile.
There are many materials with bullet proof properties including Kevlar, Lexan, Titanium, Steel and Carbon Composites. Keep in mind that "bullet-proof" is a relative term. Armor-piercing bullets are designed to be able to penetrate most of these so-called "bullet-proof" materials that will do a decent job of stopping normal (non-armor-piercing) rounds.
Armor piercing ammunition is commonly black tipped.
An armor-piercing shot was a variety of solid metal projectile with no bursting charge, in use mainly during World War II.