Agreed @grizgal it is a relatively dynamic/ambiguous metric (mining break-even, that is), but I'd read an estimate that tried to come up with a global average mining price, rather than purely based on US electrical prices. The estimate was in the $4-5k range. Cannot recall the link to provide here, but it seems to coincide with the link @jrcornel provided above citing sub $6k lows in store.

In this entirely nascent, subjective market I will stick to sub $5k bottoms, purely from a psychological standpoint.