Not only is that free, but I can't imagine a better alternative. And they would have the same issue with allocation on prem. WithOUT tagging and Cost Explorer.

That doesn't work in all cases. I've recently come across two examples where we had a hard time explaining our costs even though we extensively tag and even have fine-grained AWS accounts:

• Some costs can't be tagged or at least not easily, e.g. custom CloudWatch metrics.
• For some resources it makes a lot more sense to provide them centrally for multiple services at once, e.g. NAT gateways or load balancers.

There's a lot of overlap of features. For example, we have a serverless function that does one thing for a dozen different departments, as well as for affiliates. Right now, our solution is just to say its part of the "operating expenses" bucket, which is our black box of things that just need to be paid.

The solution to fix this would be to split the function as separate instances, to get cleaner tag data.

But now you have separate instances of the same code and everything is even less efficient/effective, and significantly more overhead for "cleaner" tagging.

The serverless function is a extreme tiny example. Multiply that by bigger projects/critical architecture/etc.

For our company, we accept not really knowing the exact details, because the cost of getting that clarity is a magnitude more work for little gain.