Got a PC who's taken the Holy Gun Paladin archetype from Ultimate Combat. Everything was fine until they encountered a few fey, and the guy started wanting to craft cold iron bullets for himself. Well that's fine, but damn Paizo doesn't tell you have to do that. My immediately though was "Oh, it'll just be twice the amount of a regular bullet, so 2 gold." That's how it should be. One bullet = one gold. An adamantine bullet is 61 gold, and when you make ammunition out of adamantine, it's +60. Perfect. That was until I noticed that a silver bullet... a single silver bullet, was 25 gold. How?! Ammunition made out of that is +2. It shouldn't be any more than 3 gold. Is this a type? Even a light weapon made out of silver is only +20. Where the extra four gold coming from?
So my question becomes, how do you come up with the proper bullet costs for the bullets? I was thinking of just making the PC pay 10 gold for each cold iron bullet. If you look at the pitted one, it's 5 gp. Figured that might be a decent base to have things run from. But even with that, I'd like to know how you do this up proper. Especially when you look at particular metals that say they're +1500 on a regular melee weapon, but don't mention what it'd be on ammunition. Maybe +1500 for 30 bullets? Then it'd just be 51 gp per bullet for base cost?