So there are different prices indeed, however, they refer to different products.

The cheaper prices you refer to are the prices for the user managed storage.
Every user can add Drive storage at this price via his/her account using personal Google Wallet account.

However, this is the consumer version of Drive, i.e. the user has to buy it with his own credit card/bank account, there is no SLA, no support, and no admin management.

To summarize the advantages of Drive Business Storage:
- 24/7 Support
- 99.9% Uptime SLA
- admin/reseller managed
- centrally billed with all your other services

It's important to distinguish between Business storage, which is purchased and managed by the admin/reseller, and Individual storage, which is purchased and managed by the user. These two different storage types don't have the same pricing structure. Additional information is at

Here is an article that explains better is the purchase is made from the user and this other article will give you more information if you would like to purchase the storage as an administrator/reseller