Purchasing extra iCloud storage?

[ICON5o2]

I'm wanting to purchase extra iCloud storage. I use my main Apple ID for purchases. It's wanting me to add a separate payments method from my main Apple ID.

Is there a better way to do this or do I have to have two payment methods? One for my main Apple ID and one for my @iCloud account?

 

[rctlr]

I think the iTunes account details are separate from the iCloud ones, so when I upgraded mine to 20gb - I used the same card details.