One irony of recent editions of D&D is that the models for magic item crafting in 3e/4e and 5e are so wildly different and yet I feel both got it wrong.
In the case of 3e and 4e (and Pathfinder), crafting a magic item is mostly a matter of having the money, some easily-gained feats, and some downtime. It's a very 'industrial' process, it's more suited to accounting on a spreadsheet rather than actual gaming, and it's both deadly dull and (almost certainly) unbalanced. (In fact, the ability of Wizards to easily craft themselves scrolls and wands is one of the aspects of 3e that most unbalances the game - it's trivially easy for a Wizard to craft lots of 'utility' scrolls and thus bypass the Vancian casting limits that are the sole balancing factor for the class.)
In the case of 5e, the pendulum has swung almost entirely the other way - magic items are basically something for the PCs to find while adventuring, and are basically not to be bought, sold, or crafted. Which is fine, so far as it goes, but does mean throwing out an aspect of the game that was, at least in concept, pretty cool.
I want PCs to be able to craft items. I just don't want them to trivially craft lots of items, or for those crafted (or bought) items to totally negate the point of adventuring to find those items.
I was musing on this while playing "Lego The Hobbit: The Video Game", where at least a part of the answer came to me. In that game, in addition to collecting the usual studs, you can collect various types of loot. These are later used to craft various items to help you in your quest.
"Hmmm..." I thought.
So, I'd be inclined to break the materials used for crafting items down into four... only one of which can be bought:
- Gold: Used for the purchase of mundane supplies and services, this is the basic building block for crafting items, and remains a half of the 'purchase' price, as before.
- Special Materials: These are rare and undefined magical ingredients of a permanent nature: mithral, adamantium, orichalcum, unobtanium, special crystals, runes, and so on and so forth. These are used in the creation of all permanent magic items, and can be found on adventures but can't be bought in any meaningful quantities.
- Reagents: These are rare and undefined magical ingredients of a transitory nature: special liquids, crystals charged with magical radiation (that will fade), and so on. These are largely collected from slain fantastic beasts. All magic items require at least some reagents, but they're primarily used in crafting potions - reagents last until the next period of downtime and then become useless, but are easily transformed into potions and other alchemic items. (And, likewise, potions and alchemic items can be broken down into reagents, but at a cost.) As with special materials, reagents can be found on adventures but can't be bought.
- Lore: This is, simply put, the knowledge required to craft the item. But, since every item is unique (and because there are no universal "laws of magic"), each item requires an expenditure of lore that needs to be repeated each time. Lore is, of course, found by tracking down books in adventure hoards, but can also be gleaned by studying with dragons, ancient masters, and the like. And, of course, those who are members of "crafting classes" (notably the Artificer, but probably also the Wizard and Cleric, and perhaps all dwarves) can count some or all of their level towards the lore requirements for every item they craft.
The consequence of this is that it adds three new treasure types to the game, which is of at least some value by itself, and also usefully ties into some of the themes of the game. But it also means that the players gain some flexibility as to which magic items they gain (freeing the DM from "wish lists" or players trying to track down specific items - if they really want something, they can go ahead and make it). But, also, since the casters can't simply churn out huge numbers of scrolls easily (due to their limited supply of materials), this should be less destructive to the game than is currently the case.
That said, it has one big weakness - the game would then require breakdowns of the costs in materials, reagents and lore for every item, would need these three items added to the treasure lists, and would also require guidelines for harvesting reagents from slain fantastic beasts!