I did the same on October 28th, 2005, for the release of The Burning Crusade, and again on November 13th, 2008 for Wrath of the Lich King.
My account has been inactive for exactly one month to date since the original release (and not by choice, I assure you). I estimate, all said and done, that I've spent somewhere around $900 between box purchases and monthly fees.
I also spent $6.50 on a Blizzard Authenticator. They didn't even charge me shipping.
They work, and they're worth it. If you possess six dollars and fifty cents but not a Blizzard Authenticator, ur doin it rong.
(EU doods: This is your link. It says they cost EUR 6,00 or £4.80. I don't know what that means but I'm betting that's not much either.)