It looks like the Warforged Nightmare isn't available on the website yet, but it appears to be live in game in the US. This mount costs $30, which is $5 more than the usual $25 price.
You really have to love Blizzards Capitalistic spirit. THey have designed a mount for the ground (yes I know it can probably fly) and they charged a $5 premium for it. I have to wonder if the extra cost is to offset the refunds they are going to have to give on the flying mounts they sold.
I know there are multiple instructional guides on how to return your pre order of WoD across this forum and wows official forum. What would be really helpful for people is to know how to return their flying mounts. I never bought one so I cannot help.
You go Blizz... I do love your passion for squeezing every possible cent out of your customers. It is almost an art form.