Unlike AWS GCP has fewer options and I would argue nothing would fit out of the box. App engine is a PaaS that has various limitations and constraints that can take significant amounts of dev time and customer support time to get through. Spot instances require ops work, as would something like GKE combined with horizontal autoscaling via kubernetes. Their best bet would be to identify hot paths in the code base and move them to cloud functions at the cost of latency then scaling down the servers.

Often in cloud computing it’s dev time, ops time, cost savings, choose one.