Just because you're using managed services doesn't mean it's going to be considerably more expensive, when you consider labor costs, and general reliability.
Your service will likely be more reliable if you use DynamoDB or AuroraDB. Your service will probably be more reliable if you build it in a way that assumes nodes will die at any point, will automatically come back in, and can scale up/down. It'll likely be more reliable if you use SQS rather than your own message bus (and let's be honest, it'll probably be cheaper too).
Yes, you should always evaluate the costs, but reliability and the amount of time you're going to spend maintaining something is something that somehow always gets left out of these evaluations.
Your service will likely be more reliable if you use DynamoDB or AuroraDB. Your service will probably be more reliable if you build it in a way that assumes nodes will die at any point, will automatically come back in, and can scale up/down. It'll likely be more reliable if you use SQS rather than your own message bus (and let's be honest, it'll probably be cheaper too).
Yes, you should always evaluate the costs, but reliability and the amount of time you're going to spend maintaining something is something that somehow always gets left out of these evaluations.