Definately all prices will 80-90%down
The world would be unrecognizable and if it ever got to this sort of state in most countries then we would likely be in the midst of world war 3. Your idea that prices would be 80-90% down is meaningless, because at that point half the people would have no money to spend and be descending into absolute poverty. Governments would collapse as the tax receipts dried up, public services would be severely depleted and infrastructure would start to be neglected, falling into disrepair. Most advanced societies really struggle if they in the worst scenarios hit 20% unemployment and it can really drag development back in time at this level. Anarchy would start to descend, with supply and demand seriously out of whack.