We had a system (Jenkins job on a cron and some bash) at my last job that would turn them off at night. We then provisioned aws keys that could manage the power settings. That way devs could power them on/off as needed.
At my current place we have an older set of VMware infra that is used for this. Cap vs op expense, they are not powered off.
Gitpod (https://www.gitpod.io) is a great option here. It aims to remove the ops burden, provide a great developer experience and give you tools to manage your spend (eg automatic timeouts, suspend/resume, standardized creation of environments).
Full disclosure: I’m one of Gitpod’s co-founders.