I'm sure you think me crazy, but that's what I was aiming for. I want people to be able to say, like _delirium and wwortiz did, "this is clearly a reasonable price because he's using S3 for backing storage and we know how much S3 costs".
A critical part of trust is transparency, and in the long term I think I'll do better by having transparent and obviously reasonable pricing than by obscuring things and trying to maximize my (short-term) profits.