How big is the app? How much usage will it get in staging?
If you spin it up on a t2.micro, the extra cost will be negligible, especially if you use auto-shutdown or Terraform to only have the box running when you need it.
It's critical to have separate environments for staging and production.
Finally, consider dockerizing your app if you can. Much more ...
You can approach this case with multiple ways.
For example you can set an auto-shutdown for 20:00 pm and auto-start for 8:00 am.
Use Terraform to create your environment and, after deployment/testings, you can easily destroy it, saving your costs.
And many other ways.
I commented on paths that you can follow, so you should choose one that brings you ...
You can use kustomization to run kubectl commands/apply files and can achieve the deployment.
However if you really want to get into the k8s ecosystem you can have look into the various tools available for a more controlled deployment workflow.
Packaging:- Manage/package your k8s objects.E.g Helm,jsonnet
Helm Repository:- Centralised helm chart repository. ...