Price check on a World of Warcraft serial key?

I made a trial account, and i'm already maxed on everything that I can do and the game is boring. I bought a 60 day game time card, and it doesn't work on making me a member because i'm still a trial account and I have to own the game before I can use a game time card.

This is the one I need a serial number for: http://screensnapr.com/v/NMWrJV.png


My question is, how much would it cost to buy a serial number from someone using RSGP as a payment, since I don't have a paypal or credit/debit card.

EDIT:
Not sure if it's needed information, but i'll need a US one.