I've got a $25k bill right now because I had enabled data-plane audit logging on an sqs queue that about a year ago I had wired to receive a real-time feed of audit events. So for every net-new audit event there would be an infinite loop of write events to follow. My average daily bill is about $2 on that account and has been for nearly ten years. It suddenly ballooned to $3k/day and zero warning or intervention from AWS.