I mostly have an Azure background but we absorbed a country that ran on AWS. I did an audit of all of their infrastructure this fall, and found they were over spending on AWS by 90%! I wish I had been tasked with it sooner, it could have saved the company hundreds of thousands, that's a few new hires, I was shocked at how mismanaged it was. It seems like the person that set it up was not familiar with cloud pricing models. For example, there were 100 or so detached disks that hadn't been touched in a year or two, which of course isn't free. The instances were too big, etc. I've always found Azure's billing to be easier to maintain cost controls over (at least it feels more friendly.) I wonder how many companies unintentionally over spend on cloud services because of the lack of understanding of the pricing models.
