You can find a list of our prices here: https://cloud.google.com/compute/#pricing . Preemptible VMs have flat per-machine type pricing compared to EC2's bidding-based pricing. For example, a Preemptible n1-standard-1 is 1.5 cents per hour in the US and a preemptible n1-standard-4 is 6.0 cents per hour.
