Chars transfer.

Hi there.Couldn't find any answer so i thought to create this topic.
So,i have a premium account and a non-premium account. I'd like to trasnfer all the chars from the non-premium to the premium one both on Cata and MOP server. Is it possible to do? Does it cost any coins/point or is it free?
Thanks for your time,best regards.

You can only do this through trade, which requires Premium and will take you a certain amount of coins as fees.