You can always buy a new account. But you dont have to.

If you make a character on a PvP server then delete him you'll be able to create a new character on the opposing faction. Level him for a while then ticket a GM.

When the GM (read: finally) responds to you make up some bullsh!t. What i said was that my brother deleted my other character while i was on holidays. The GM will be more than happy to let you know that "there are only a certain amount of times which a GM can help with character restoration" blah blah blah...

The next time you log in you should have alliance and horde on the same account. I'll post a screenshot of my character screen when i get home from work.

What ever you do don't bank/sell your stuff before you reroll. You wont get it back.