The price as the time writing this review is $23 for 2 months, that gives you about $11.50 per month. The cheapest you can get from WoW official website is $12.99/month, only IF you pre-paid for 6 months.
So pre-paid for 2 months at $11.50/month vs pre-paid 6 months at $12.99/month, you do the math.
I had to say I was a little bit turn off by what Blizzard did to me few minutes ago, I posted on their forums the link to this Amazon deal, it was deleted in 3 minutes. I know they're trying to protect their monthly fee, but it's kind of childish and immature, IMO. Just let you guys know here, you're the judge.