Maybe instead of cost reduction do a rebate?Cosmic Orrey4Whenever you cast a spell, add X mana to your mana pool in any combination of colors of that spell, where X is half that spell's converted mana cost, rounded down.Cosmic Orrey4ArtifactWhenever you cast a spell, put X charge counters on CARDNAME, where X is half its converted mana cost rounded up.Remove a charge counter from CARDNAME: Add C to your mana pool.
Chip suggested on Twitter:"Is there a way to approximate "half" without rounding?Each spell with converted mana cost 6 or more costs 4 less."That's a pretty clever angle.
Or double mana production :)
@Jack nice, haha, that'd do nicely.