We solved that exact problem with our open source tool Resoto. Specifically our "Defrag" module, which cleans up unused and expired resources:

https://resoto.com/defrag https://github.com/someengineering/resoto

The magic behind the clean up is Resoto's inventory graph - the graph captures the clean up steps for each individual AWS resource.

One of Resoto's users, D2iQ (now part of Nutanix), reduced their monthly cloud bill by ~78%, decreased from $561K to $122K per month. There's a step-by-step tutorial on our blog how they did it.

I don't mean to hijack Dashdive's thunder here though, congrats on the launch!