Hi there, with the MERN stack we can use ECS(provided by AWS) to deploy applications as docker containers so that we only use a minimum amount of resources (thus minimum cost) while also making the whole system highly scalable. Also, the CI/CD pipeline can be implemented using CodeCommit/GitHub, CodeBuild, CodePipeline and Cloudformation which are provided by AWS, thus easy to manage and maintain using Cloudformation to ensure every change along the whole process is consistent and transparent.
Also, just wanted to add that I have done a lot of AWS related projects in Freelancer and please feel free to contact me if you want to know anything.
Regards.