• CA - Cluster Autoscaling.
• VPA - Vertical Pod Autoscaling.
• HPA - Horizontal Pod Autoscaling.

To me, using VPA/HPA alone can’t be much cost savings. At best, it can rearrange the resources you are already paying for to be more efficiently used. That’s good, but if you want to keep costs low, you would need to implement CA as well, and then keep everything as lightweight as possible until the hits start rolling in and it automatically scales up. When the hits subside, it scales down to the "normal" setting.

That's my current understanding.