Old One said:
Yeah...that Old One is a total hack...yep, sure enough. Just add the d20 Economic System to the long line of brilliantly-conceived, shoddily-implemented ideas rattling around in my mellon

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~ OO
PS -
<Old One busily begins upgrading the desert scorpion swarms for the NC Gameday VII
>
I knew that would lure you into this thread!
On the matter of "rare magical components" for making magic items, I use a version of this in my game but it goes hand in hand with the existing system with no need to modify the existing costs of magic items.
Essentially, I don't like the idea that you have a pocket full of gold pieces and you spend a day in the wilderness "brewing a potion" and the next day you have a potion and your pocket is not full of gold pieces. In my campaigns, you cannot simply spin gold into magic.
That said, it is not hard to find the ingredients to make most magic items in a town of any real size. So I'm not saying, "You must have a Troll's kidney to make that potion." I'm saying, "There's a Wizard in town and he sells Scroll Ink and the components necessary to make Potions or Wands but not Arms and Armor or Wonderous Items." Then the party Wizard might say, "I'll buy 300 GP worth of Scroll Ink, 200 GP worth of Potion Components and 750 GP worth of Wand Components." He writes that down on his character sheet, spends the cash and now, when he's out in the field, he has enough of these ingredients to make that amount of magic items.
I find that this lends a certain level of realism that makes me and the players happy. And it also gives me a new sort of treasure I can hand out. Instead of saying, "You kill the Ogre and find 500 GP." I can say, "You kill the Ogre and discover that in addition to 200 GP, he's collected some magic mushrooms that are worth 300 GP in Potion Ingredients." I can even get fancy and say, "You kill the Ogre and discover that in addition to 200 GP, he's got some Greentop Mushrooms that are worth 300 GP in Potion Ingredients but are worth double that for making Potions of any Transmutation spell."
If I want to occasionally have some part of a critter they fight (we're back to Troll Kidneys and Basilisk Eyes here) be worth something toward item creation then I can do it. But when the PC's are in a city then they can effectively convert cash into magic items because the components are freely available. Right now I'm running an Eberron campaign in Sharn so this is more or less the way things operate but I've established the underlying system so the PC's won't be stunned if they fight a critter in the bowels of the city and discover that its horns are worth 100 GP toward crafting Wands. They can either use it for that purpose or sell it to a local Wizard. Either way it is valuable loot.