I tried one, that gave me 87.
Then I tried this one Consecrated Spike
This one gave me 127 Ash. This Item cost 4.500G
Obliterum goes for 7k.
This may vary on your Realm, but if you have time to test all Relicts (maybe even the Greens), you guys may post the Item and how much Ash you got from it.
Hope this helps and don't make it super public so fast, so we can gain a good amouts of gold. :P