Can you transfer funds from your battle.net balance?
They don't support cashing it out in the normal sense, as Blizzard will not transfer the balance to a bank account for you. However you can link your account to a Paypal account, and "cash out" your balance to that - this is what the Diablo 3 FAQ is referring to. There is a 15% transfer fee on that.
This is also not a universal solution. I believe there may be region/country-specific restrictions on Paypal allowing cashing out of your balance.