If they are using S3, then their storage cost is close to 100% variable. Assuming their rate of paying customers stays consistent with their free customers, regardless of how much they grow, isn't it safe to assume that their model is tailored to at least cover their cost of storage with their revenues?

If that wasn't the case, it might be hard to justify giving them more money, unless they were very close to break-even on that cost. So I'm assuming that they're bringing in enough revenue to cover their storage cost, regardless if their storage cost is 100k / month, 5MM a month, or even higher.