I kept it the analysis to GCE only for simiplicity. (both because the costs of spot instances are highly variable, and costs are not prorated on Amazon meaning you have to pay for the full hour; an additional concern if you just want to run a small ad-hoc training)
If a spot instance terminates in the first hour you're not charged for it. You can grab spot blocks as well for specific duration workloads.
This entire article was about spot instances. On GCE they are called preemptible.
Didn't catch this thanks, spot instances have a bit better rate, but as he mentioned they are billed by hour :)
Yes premptiable are a much better deal with minute billing.
For shits and giggles I recently compared a spot instance CPU miners of monero vs spot instance GPU miners. I don't have the exact numbers on hand but IIRC the CPU miner was ~50% the cost in terms of $/hash.