While managing my company's AWS EC2 usage account, I found out an "unexplained" spike in daily cost on the Billing Explorer. It was a jump from $12 to $39 USD.
Going into the "Cost Explorer" or general AWS billing info only showed a bump in the "EC2-Other" category. However it was a bit difficult to find the right way to "drill down" into what other EC2 usage was causing the cost increase.
As seen in the image, to get the detail of what the "EC2-Other" comprises in the AWS Cost Explorer interface, you have to select the EC2-Other service in the filter category and then select the "Usage Type" option in the Group-by setting.
In my case, the increased cost was due to one single 1TB disk which I had changed from gp2 into provisioned io, and increased the IO from 3000 to 16000.
If you think about this, AWS is a dangerous place that can byte you back in the wallet if you are not careful or you don't know what you are doing.
I've heard other horror stories of people spending thousands of dollars because of the lack of some planning (like, sudden spike in Lambdas processing!).