It hurts more at the start of tiers than the end strangely.
A level 5 item is 1,000 gold.
A level 15 item is 25,000 gold.
So this makes it look like half an item at the midpoint of heroic and 1/5 of an item at paragon.
But an item is 5,000 at level 10 and 9,000 at level 11. So it jumps from 1/10th of an item to more than half in a single level.
Just a weirdness from having the cost jump by tier. It does become overall a lower percentage of wealth as you get higher, but people are relativity more expensive to raise at the start of tier than at the end.