The cheapest source of Heavenly Shards comes from Disenchanting (DE) Stormforged Shoulders. The great thing about these are that they have a 100% chance of DE into1-4 Heavenly Shards.
You’ll need access to a Miner & Blacksmith to craft these.
8x Obsidium Ore turned into 4x Obsidium Bars tuned into 2x Folded Obsidium (Blacksmith).
16x Elementium Ore turned into 8x Elementium Bar.
Cost to craft = 54g
8*2.25 = 18
16*2.25 = 36
Due to Bountiful Bags I regulary get 2 extra Heavenly Shards per 10 DE’s at a minimum.
So if I were to DE 50 Stormforged Shoulders I would expect a minimum of 60 Heavenly Shards
(50x54g)= 2700g/60 = 45g ea
Sales 60*70g = 4200g
The other source of Heavenly Shards is from Maelstrom Shatter where you’ll get 2x Heavenly Shards per Shatter.
The problem here is that the cheapest you can get Maelstrom Crystals on a regular basis is 146g from DE Sleek Flamewrath Cloak source www.wow.joystiq.com so unless your Server sells them from less than 90g each you’re better off crafting Stormforged Shoulders.