Great catch, simonw (and everyone else in this thread).
I've reviewed some other static hosts and settled on wasabi for now. When my S3 bill rolls in, I'll reply to this comment with the damage. A scary number will help others avoid my oversight.
AWS Billing reported that I was charged $28.43 over the course of 7 hours, for a total transfer of 306.916 GB. I believe this capture the ~25k page views the site received before I switched over to another static file host.
Lesson learned for me. Thanks to everyone in this thread for saving my wallet.
I've reviewed some other static hosts and settled on wasabi for now. When my S3 bill rolls in, I'll reply to this comment with the damage. A scary number will help others avoid my oversight.