What would be a really nice way to charge for bandwidth?

According to the Cloudflare blog post AWS's Egregious Egress, it costs AWS around $1.20 per TB of traffic transferred: https://blog.cloudflare.com/aws-egregious-egress

Basically, Cloudflare says: If you run a 3mbps link at 100% utilization for a month, you'll have transferred around 1TB of data. If it costs you $1.20 to use the 3mbps link for a month, then you're effectively paying $1.20 per TB.

I think this would be a really nice way to charge for bandwidth. 

Instead of charging a monthly price for bandwidth, it would be nicer if customers could simply just buy a certain amount of bandwidth that never expires.

It would be nice if I could just pay $50 up front for 50TB of bandwidth, and that bandwidth would never expire, so that I can use it whenever I want.

I think that would be a really nice pricing model. I wonder why VPS providers don't use it.

Actually this is how a lot of prepaid SIM cards work - you can get IoT SIM cards with data that won't expire for 10 years. Pretty neat concept.