I'm hosting a photo sharing SPA on S3/Cloudfront/Lambda with a robust user system including email verification, and a few GB of image files, and I pay $0.25/month at most. Yeah, it's a personal/friends-only site so it doesn't see much traffic, but that was kind of the point - I wanted to pay next to nothing for this site if nobody visits it, and it is working well for that. $3.00/year is pretty cheap.