Have you had a chance to look at Google's Preemptible VMs? They're a fixed 70-80% off of list price.

Another point is, Google's VMs are generic CPU/RAM combinations. You don't need "network optimized VMs" or "storage optimized VMs" - you simply get those things on any VM. This makes the "excess instance supply" market much more fluid and simplifies folks' lives.

Happy to discuss further!

(work at GCP)