Alternatively, if you don't want the ability and risks associated with being able to scale to solar system size - use a different vendor who isn't focussed on providing that.
Amazon AWS's "important customers" are not "fallible human beings" who plan to keep their monthly spend under $100. They'd perfectly happily inconvenience thousands of those users in favour of their customers who _do_ need solar system scalability.b(And, to their credit, there's an abundance of stories around of people on typically 2 digit monthly spends who screw up and get a 4 digit bill shock - which Amazon reverse when called up and pleaded with.)
So they built their thing as "default unlimited". Because of course you would in their position - follow the money. When Netfix wants 10,000 more servers - they want it to "just work", not have them need to call support or uncheck some "cost safety" checkbox.
If you need "default cheap", AWS isn't the right tool for you. You can 100% build "default cheap" platforms on AWS if you've got the time/desire (well, down in the "I can ensure I don't go over ~$100/month - it's not real easy to configure AWS to keep costs down in the $5/month class - the monitoring and response system needs about twice that to keep running reliably).
I sometimes don't think people (especially peope who "grew up" in their dev career with "the cloud") understand just what an amazing tool AWS is - and the fact that they make it available to people like me for hobby projects or half-arsed prototype ideas still amazes me. I remember flying halfway round the world with a stack of several hundred meg hard drives in my carry on - catching a cab from the airport to PAIX so I could open up the servers we owned, and add in the drives with photos of 60,000 hotels and a hardened and tested OS upgrade. Buying those 4 servers and the identical local setup for dev/testing, getting them installed at PAIX, and flying from Sydney to California to upgrade them was probably $30+ thousand bucks and 3 months calendar time. Now I can do all that and more with one Ansible script from my laptop - or by pointing and clicking their web interface.
AWS is an _amazing_ tool - talk to some grey-beards about it some time if you don't remember how it used to get done.But the old saying holds: "With great power comes great responsibility." If you don't want to accept the responsibility, use a tool with less power. Don't for a minute think Amazon are going to put a "Ensure I don't spend as much money with AWS as I might otherwise" option in there - if there's _any_ chance of it meaning a deep-pocketed customer _ever_ gets a false positive denial from it. (WHich, now I think about it - makes this new Lightsail thing make so much more sense...)