Let's give 1 billion names 1 mb of storage each. (pretty unlikely high, right?)
So you've got to deal with this 1 billion mb of data.
Let's convert to GB cause that's how everyone charges for storage.
1 billion mb => 1 million gb
https://blog.cloudability.com/aws-s3-understanding-cloud-storage-costs-to-save/
Let's round up and say AWS is doing it super cheap... Instead of $0.02 per gig, you hate AWS and build your own and you to pay $0.10 per gig per month of storage.
1 million gb * $0.10 storage per month * 12 months in a year = $1,200,000 a year in storage costs.
That leaves you $998,800,000 to split with the registrars.
Unless I'm missing a zero or few somewhere, it seems ok.