Question about upgrading world of warcraft cataclysm trial to full.?

Hi my world of warcraft cataclysm trial has expired and i would like to get the full version. I have never played wow before this and would like to know how much i would have to pay to continue playing. When i go to the manage account setting on battle.net it says i have to pay 19.99 to upgrade to the full version. Is this the base version of wow i will be upgrading or cataclysm? When i downloaded the installer it downloaded WOW the base version, burning crusade, wrath of the lich king and cataclysm in that order and installed them. On the account settings i am also seeing the upgrade through to cataclysm option for 87.99 so i am a little confused. If someone could walk me through the process i would be very grateful because i don't want to end up wasting any money. i just want to get on with playing cataclysm with the characters i created in the cataclysm trial. Thank you please get back to me soon. :)