A few years ago, when I was kinda active in the startup scene in my area, you have people selling access to cloud credits with penny-on-the-dollar price. The credits are given out liberally to big-corps, organization by AWS/GCP, through workshops, webinars, events. All in the hope of roping the departments into building MVPs, demos on AWS/GCP, but people also find a way to cheat on that system and make some quick bucks.

I know a startup of my acquaintances that have been running on AWS for 5 years straight without paying a single dollar to AWS. When the credits almost run out, they started to migrate their data over to another account with credit. That happened twice already.

It helps to have a portable, replicable IaC config. But also this is sustainable because they are a pretty small struggling shop. You will probably not be able to do this if you are trying to maintain more than 3 nines for an enterprise client.