I would say a heroic is worth 3 shards, 1 void, effort, and chance of boe's.
My math and opinion:
3 shards = 100g
1 void = 50g
rest of the loot = 100g
effort = 200-500g depending on which zone.
total = 450g-750g per run

I would add in an extra 250g for a timed run with mount loot.