I wouldn't be too quick to say it's too expensive.

My set up is not dissimilar to your own. I'm comfortable working on the command line, using s3cmd to sync the site, modifying bucket policies, etc. Once you know those things - or if you enjoy learning them - it's all pretty trivial, but if you don't... well don't underestimate the hassle for someone who doesn't know this stuff. I'd think it a waste to pay $13/mo for what I'm happy to throw in an S3 bucket, but that's 3 venti lattes for someone not to have to deal with any of it. It's not the file storage they're charging for.