[23david]

I've been working with a client in a similar situation recently, but instead of building a custom solution we went with customizing cloudhealth (https://www.cloudhealthtech.com).

It's a complicated tool for sure, but once it was all set up we finally had visibility into a complex multi-account AWS spend, and could start generating automated cost reports for each company business unit and major customer.

I wouldn't recommend going to the effort of building a custom setup... AWS billing is just too complicated and it changes frequently to add even more layers of complexity. As one example, the recent change to add RI size flexibility completely changed the calculations for RI costs and recommendations.

I've also used cloudability and cloudcheckr in the past, but both systems had serious drawbacks. In my opinion cloudhealth is a much more advanced/professional system at this point.