Heroku + Paperclip + Amazon S3 - Pricing?

Since Heroku is a read-only filesystem I can't use paperclip to store a small quantity of files on the server. Database image storage is an option, but not particularly ideal since that may crank my client's DB size up from a few hundred KB to over the 5 MB 'free' shared DB limit (depending on size of images).

That leaves Amazon S3 as a likely solution. I understand that Heroku is hosted on EC2 (I believe?). Amazon's pricing wording was a little bit confusing when referring to S3-EC2 file transfers. If I have my client setup an S3 account and let them do file transfers to and from there, what is the pricing going to look like?

Is it cheaper from an S3 point-of-view to to both upload and download data in the rails controllers, and then feed the data to the browser using send_file? Or would it make more sense to just link straight to the image or pdf from the browser like normal?

Would my client have to pay anything at all since heroku is hosted on Amazon? I was looking for other questions related to this but there weren't any really straight answers concerning which parts of the file transfer would be charged for.

I guess the storage would cost a little (hardly anything), but what about the bandwidth? Thanks :)