Fotget about the treasure and pricing system of 5E!

[Mikal]

That is 3.x thinking that I and many others fundamentally disagree with. The rules for two different people doing the same thing do not have to be the same when there is substantial differences between who and what the characters are. The rules are not a physics engine for the world, and them not working identically for everyone is a feature, because not everyone in the world is an adventurer.

Great, so explain to me how Wizard A can make a 9th level scroll for say... 1,000 gp, while the PC who actually is a better wizard must spend 500,000.

Or, if you must have an explanation, you assume that the level of expertise a dedicated craftsman has allows them to create things for less, and that the numbers provided in the optional crafting rules have the costs of expected errors due to lack of expertise built in.

Great. Now instead of adventuring, my wizard PCs retire to a small laboratory to save hundreds of thousands to millions of gold pieces in expenses, and my campaign is thrown into chaos because NPCs get things PCs don't that said PCs should logically get as well. Yeah... I think it's better if both types of characters had a more even playing field, personally.

Besides, are you tracking NPC wealth? Who cares what it costs them. It's irrelevant to gameplay.

If they're making items which would cost several hundred thousand to several million gp, and are actually making said items? Yes.
Just like I don't put monsters in a specific dungeon room without a reason, I make sure any NPCs who are making items which cost X amount have the resources to do so, and have those resources change accordingly.

Allows those investigation based PCs something to chew on if they're trying to link Lord Whoever to the Death Cult when they realize that the resources he has are being lowered in an amount commensurate with what was needed to build the Altar they smashed last week before it summoned the Pit Fiends. And that's not the only way for the PCs to find this out. I run a sandbox, living world with several ways for PCs to inventively find things should they try, with interconnectivity vs. DM fiat and/or railroading.

If you're just murder-hoboing your way through life as an adventurer, granted, it's irrelevant to gameplay to keep track of NPC net worth except at the time of their death by PC hands, but as I stated, I don't just go from raid to raid with my group when I DM.