My org made a similar transition. It's hard to articulate exactly precisely how much we saved as our "production" or revenue generating environments are roughly the same.

We transitioned out of AWS where we had relatively well managed instances of our stack managed with chef and terraform to GKE in Google Cloud where we migrated to a helm chart and custom orchestration tooling on top of that.

Prior to the migration I'd say that 80% of our instances were idle. Currently, all of our k8s nodes with 16 cores are running with an average load 5-7. We try to keep enough headroom to prevent any waiting or queuing, which is an entire medium blog post unto itself.

So, roughly the same or a little more "production" workload, but the number of non-prod instances of our stack quadrupled. Anyone in the org at any time can spin up an instance of the stack for a custom sales demo, to debug an issue, to test a feature, or anything else. There was a great deal of pent up demand that nobody expected and which caused my team to thrash a bit to catch up to when we made the transition.

All in all, our GCP spend is about 20% less than our AWS spend was. We're getting a lot more utility for a little less money.