cloudflare is not charging different amount for different storage providers, some storage providers are waiving the fee when the upstream is cloudflare.
As far as our service is concerned everyone pays the same price for B2 Cloud Storage, $0.005/GB. We're not a network provider and in this case neither is Cloudflare. We are both service providers. The partnership between us simply allows people to move data between us freely, but you still need to pay Backblaze B2 for the storage of the data, and you need to play Cloudflare for the distribution!