This is impossible to even ballpark without some insider info. My company for example runs a ton of user facing services on AWS, but the vast majority of costs come from internal data storage and processing pipelines (server logs, analytics, BI/SI dashboards).
Since I'm a team of one working on some Amazon services for a far smaller customer base, I get a broad slice of different technologies and problems to solve. I can't imagine being the person whose job is to manage some slice of the part of the stack that monitors just the billing portion of their aws usage.<p>But contemplating that scale also makes me better understand how these companies end up with hundreds of engineers to manage a product that on the surface really doesn't do a whole lot.
I've got to think bandwidth is their largest expenditure... even with all the CDN infrastructure they have in place.<p>AWS bandwidth is extremely expensive - regardless of the negotiated discounts they probably get.
I just hope someone there is getting weekly emails like:<p>"Dear AWS customer:<p>AWS Trusted Advisor currently shows alerts for 12 checks (1 red and 11 yellow) and $18,922,425.23 of potential monthly savings based on your usage."