Thanks - that's eye opening.
So, what this really comes down to (after a good nights sleep) - is what type of traffic/transactions are you running on your back end infrastructure.
If the data is static, then you can probably (these days) cut your costs for 25 Terabytes/month from $8K to $800 (or, in your extraordinary case, $80), simply by being a bit intelligent as to how you make use of VPS/CDN/CloudFlare Transfer allocations.
On the flip side, if much of the data you are transferring out is the result of dynamic back end transactions, queries, and generation, then it's unclear to me that you can (easily) recognize the savings that you might see when generating static content.
I'm interested in knowing if CloudFlare will start throttling/shutting down people who pay $20 and use 25 TBytes in the long term though - that alone, for some organizations, will cost them more than the extra $8K they would pay to AWS (who, have zero problem with you using 25TB, 250TB, 2.5PB, etc...)