What are you using for compute EKS and Fargate? We just helped someone switch from Heroku to AWS and they dropped their cloud costs by 67%. This is using ECS + EC2. Fargate is typically 2x more expensive.
I probably should have clarified that the extra cost was expected as we did a lot more in AWS than we could in Heroku, we used the switch to start using bunch of stuff AWS offers like Lambda functions, CloudFront, RDS etc. Stuff that we just didn't (and couldn't) use on Heroku, thus didn't pay for it.
As the purpose of the switch was to get more control, features and out of the Herokus "black box", higher costs were expected and perfectly normal.
