Here is what we came up with.
A player has dragonhide he would like to craft into halfplate. We wanted to figure out what the cost of the raw dragonhide would be in order to figure out the price he would have to pay since he had his own materials, mostly.
I went ahead and tallied the average cost of the armor that would be possible out of a size G dragon. The average cost would be 1,022 GP. That's taking the hide, banded, halfplate, breastplate, fullplate, and 2 shields combined and averaging them; a buyer of the dragonhide may not know which suit to make yet, so all options could be covered and make a profit.
Since the character has the dragonhide material already, I would subtract 1,022 from the total base price of the halfplate, bringing it to 478 GP. Now the character can take 1/3 of that for crafting, costing roughly 160 GP.
I would say the most logical answer would be to subtract the cost of whatever materials you already have on hand. Of course, then you get into the issue of the material costs not really making sense, but oh well!
|Brogue The Rogue|
There are, in fact, already rules in place for this, but they're more subtle than you might think.
If you want to craft a mithral chain shirt worth 1100 gold, you need about 367 gold pieces worth of mithral. If you happen to have mithral ingots on hand, ask your DM the value of those mithral ingots in gold pieces. Viola.
The REAL question, is why the HECK are you making halfplate? :P