I wonder what it would cost?

Amazon S3 pricing starts at $0.125 per GB per month. So if you just want to store an extra 500 GB that's gonna run $62.50 per month on a HDD!

Given SSDs are 5-10X more expensive who would be willing to pay $300-$600 per month?

Serious question: Any S3 users out there who would pay 5X as much for better performance? If so, what are you working on?