I imagine Imgur now is many times bigger than we were. If I remember correctly around 2009/2010 our Amazon rep said Twitpic accounted for about 1% of data stored in S3 at that time and I think our cost was around $100k/month. We eventually got that down to $60k'ish when they gave us "special" pricing and later on we put bare-metal caching servers in front of it to store/serve hot images which further decreased it.

Disclaimer: Hopefully I'm remembering correctly, it's been a while!