What will be pricing after lowering number of CPUs while creating ec2 instances?

The instance cost is fixed per hour cost depending on the type you have chosen. So it will be 0.408/hour regardless if you disable all CPU or don't use the instance, if its powered on you will be billed for it.

You can utilize spot instances or Saving plans to reduce the per hour cost, but keep in mind the caveats of those. e.g Spot instances can be terminated by AWS on 60 seconds notice, so make sure your workload can handle that termination.