How feasible is to terminate the non-prod environments to save cost

One option is to use the AWS Instance Scheduler solution (https://aws.amazon.com/solutions/implementations/instance-scheduler-on-aws/), an AWS Solution that allows you to create schedules to start and stop of Amazon Elastic Compute Cloud (Amazon EC2) and Amazon Relational Database Service (Amazon RDS) instances. An example scenario that you can configure is to automatically start resources Monday to Friday, from 09.00 - 18.00.

This solution helps reduce operational costs by stopping resources that are not in use and starting them when they are needed. The cost savings can be significant compared to leaving instances running at full utilization continuously (up to 70%).

It is easy to deploy by following the deployment guide, can be centrally configured for Cross-Account management, or within individual accounts.

It is indeed one of AWS best practices in terms of Cost Optimization techniques, and many organizations are successfully using this solution.

I have implemented this several times for different clients, though we do not terminate we just stop instances such as EC2 and RDS

I use event bridge, step functions and lambda to perform this on a daily basis and leave environments down all weekend.

You could take it further and remove as much as you can each day and redeploy, sure. IaC would be a good way to do this.