What’s the best way to audit all resources inside an AWS account? (Need to find all orphaned ones costing money, basically)
If you login to the master account you should be able to go into the billing section and find (at a service level) all the things costing money, separated by each AWS account.
AWS-nuke can be run in a dry run mode, I hear that works for this use case
Sign up for www.vantage.sh 
The tag editor also kind of lets you list a tonne of resources
Tag Editor and billing idea has worked for me many times.
