I think you can set quotas on S3 somehow too.
You can set alerts but not hard quotas. This is a perpetual topic of debate around pretty much all the big cloud providers. They're really set up for companies that presumably don't want to "burn everything down" if they get a usage spike or screw something up. But it makes them at least something of a risk for an individual who absolutely doesn't want to wake up to a $3K bill under any circumstances.
But, yes, in general for an individual hobby site, I'd choose an option that resulted in a hug of death rather than a big bill.