Tal Rasha's Relentless pursuit or Zuni's Marrow?

[aerial]

And how exacly do you spam bears all day without blood ritual?

By using reduced zombie charger items, casting spirit walk with 30% mana regen (and resetting its cooldown with passive). Blood ritual is nice, but it is just 15% mana cost, it doesn't make the boundary between infinite and finite bears.

[Dogbert]

What is the best item(s) for reduced zombie charger cost and how much can you lower it?

[aerial]

offhand 14 i belive (can by any offhand, zuni set), very expensive with good stats
soj 10
and then skull grasp and mara, but they are usually not worth it, since it had to be on top of good crit roll, and gl finding these

[Dogbert]

Zombie bears is 140 mana. Does it really do anything reducing the cost by 14 mana down to 130 or so?

[aerial]

Of course, it is in fact much more powerful that mana regeneration per slot, because it scales with attack speed.
If you have fast endgame setup with ceremonial knife, casting bears at 2 attacks per second, for example adding 10 mana regen to your gear is twice weaker than reducing bear cost by 10, because it saves you 20 mana per second.
It is better than mana regen at speeds above 1.00, and faster your attack is, the better it becomes.