Good advice greengrl. I remember I shared a tiny apartment on the beach one summer with an ancient AC window unit and the electric bill was insane because the unit was so inefficient. Meanwhile, the apartment next door had a much newer window unit and was paying less than 1/2 of what we paid. I had to get a new AC when I owned my townhouse. It was bigger, but more efficient, so I could turn it down a few degrees and still pay less than I had paid with the original unit.
As for the roommate issue, there is no way I can have roommates again. My sister roomed with me for 3 months two years ago in a tiny sub-500 square foot apartment and we almost killed each other. I'm going to ND and if I study in London, I will probably rent a room in a house or have roommates, but that's because I don't want to pay 650 pounds a month to live on my own.