S3's the storage - you still have to run an httpd daemon somewhere, and even the smallest, cheapest EC2 instance will run you no less than $14 a month. (Notwithstanding the one-year-only free tier)
(Wow, I didn't know you could just serve content straight off the storage. I need to re-examine AWS.. thanks :D)
More likely scenario is a tiny PHP site with the database hosted elsewhere?