Honestly this is a valid concern. I am not knocking AWS and they are working with us but $100000 in one week from bad code in a Java service is really nerve racking. For the record the only reason I use AWS over other clouds is because they actually work with you when stuff like this happens. ( Its taking a long time but we are hopeful)

then use Lightsail or set a maximum size for your ec2 autoscaling group

Or stop overengineering and use a PaaS like Netlify.

But outbound traffic

Cloudflare Pages is free.

It's very odd that AWS doesn't support spending caps. A lot of other services and paid APIs I use have them, and they save me a ton of stress.

As long as enough people use AWS despite the lack of spending caps and the stress it causes, it just means Amazon effectively monetizing your risk tolerance.