I store about a terabyte on S3. It costs us $25 a month. If I spend more than a few minutes a month administering an alternative setup, I've lost money compared to just paying S3.
That entirely depends on how you use the data. If you store files that are accessed over the general internet, and each file is downloaded just once in the month, you've just quadrupled your monthly cost, thanks to AWS' high data transfer fees.
