One way to get a quick view is work out the in-ground value of...

One way to get a quick view is work out the in-ground value of minerals.
Australian projects (CLQ, COB) are around 0.08-0.12% Co. (plus by-product credits)
Cobalt price (roughly) is US$30,000 per tonne.
So at 0.1% Co (average of above) - This equates to US$30/t in ground value (of cobalt). (if you ignore credits, this means you need to be able to mine, process and transport for less than US$30/t to make money.

Depending on how you mine (surface, underground etc) - a vague suggestion is anything over $100/t probably has a good chance of working. (again - depends on how deep, processing etc)

IF EQU does really have 5% Co in ground - this is US$1500/t in ground value (which leaves a lot of room for mining/processing etc)

(this is a really quick way, I am not saying it's fool proof by any means - many things impact costs (way of mining, depth, processing, recoveries etc)