For a 5-minute1080p video viewed 100k times end-to-end, the estimated CDN cost if using reasonably performant public cloud at a blended global average might fall in the range of $900 to $1,500.

Yes you can use a junk CDN instead, or assume you don't have many viewers from Japan, Korea, SEAsia, Australia, etc. (If viewed just in the US on a low-cost CDN and doing massive volumes with that CDN provider then maybe $150 or $200).

But if it's global and the video goes any sort of viral then CDN costs may be pretty daunting.

People always focus on the storage. The storage is pennies. It's all about the CDN.