What is needed is a way to create magic items that doesn’t use a common monetary unit.

In fourth edition, terrible that it was, there was a way to use existing magic item to reduce the cost of a NEW DESIGN.  Items could be drained of their magic.  The substance drawn from the item is literally a created physical material called RESIDUUM. This substance can be bottled and kept indefinitely. It could be sold, though that's not an option in my game.  And it could be put toward the gp cost of creating any new magic item. So if you had 50,000 gp worth of residuum in a bottle you could use that instead of gold to make items.

I would propose that anyone might cannibalize any existing magic items in order to gain the power that is required to make a new magic item. Via a Ritual.  But CASTERS - who can create magic items (via the feats) - would have the ability to drain the magic from an existing item and use it directly in their casting.  This method would not create residuum; the magic is simply taken from the sacrificial magic item during the item creation process.
And it all happens seamlessly.

Each magic item contributes a gp value equal to its construction cost in the Pathfinder rules. So if a party has a Ring of Water Walking that they don’t want, they can drain it of magic and it would contribute 7500gp toward the cost of a new magic item.

The magic item creation rules can exist in exactly as they are written, and I don’t need to make tens of thousands of surplus gold pieces appear in the economy. And casters MIGHT start actively seek out caches of items in order to create new ones.  These rules don’t preclude PCs finding magic items in treasures, or in the cold dead hands of NPCs. Likewise it doesn’t stop a caster from discovering a laboratory that has 100,000gp worth of magical components in it.

My problem with magic has always been the price tag.  I can’t logically give the sort of money that the rules would DEMAND for each PC, at each level: it’s insane and economy wrecking.

But at the same time, I can’t maintain the magic item creation rules unchanged with out dispense money on that scale. While I do want to look at the power level of magic items created  - the money's necessary to craft ANY ITEM is bloody unrealistic.
Until, I can apply some method to the madness inherent in the power structures of DnD -- This is my compromise to adjudicate the lack of heavy gold economy.