Vanilla Box ($50)
Initial account was sold for $100 a long time ago (Yeah, I admit it... -$100)
Vanilla Box (again) ($50)
BC Box ($50)
WotLK Box ($50)
Cataclysm Box ($50)
6 years of monthly subscription, minus 3 months because I didn't quite start on release day ($1035)
10 months break (-$150)
TOTAL: $1035 over 69 months = $15/month
Not that bad, considering it also taught me near perfect English, pointed me towards an awesome woman whom I've been married to for now almost 5 years, and entertained me a whole freaking lot.
I regret nothing. I'm actually genuinely excited for Cataclysm.
P.S. That is only the money I spent on my account. Since July 2006 I've been paying for my wife's account as well, and she took the same breaks I took.