Okay sorry for not explaining a bit further,
Pathfinder with limited 3.5 in it

I will be letting a few (i.e. a ton) relics be recovered before the collapse of the mega(magical) city the characters lived in.

The world is a bit like Judge Dread but was a magical paradise, not a urban slum.

The Wilds (i.e. the vast unchecked land outside the megacity) is full of all the stuff in the Monster Manuals without the encounter rules, the party could theoretically have to hide from a hydra at level one.

I have been thinking of replacing spell requirements for crafting with bits & bobs from monsters as long as it is a well reasoned replacement for the spell (like a dragon's fire gland for a flaming sword)

My problem is keeping powerful relics out of their hands until level appropiate times. Logically NPC's might not care so much if someone wants to borrow this "weak, mundane" Axe of Thunderbolts & Goblin Punting. Also if you look at the opposite of that spectrum, if the NPC's now value the item, they would almost be fanatical about hording it's now unique & terrible power.

How would the impact of such a broken economy work if they happened to find a civilization out in the Wilds that has a system of currency?

How do I handle player choice when it comes to powerful items? A normal character would just buy & sell to get gold to buy the thing he really wants. The characters in this world would be S.O.L. though