Battery Full [Q] About Wifi and data and their battery consumption

Hello to anyone who read this thread

My question is, when wifi is on, and I'm connected to a network, like home, work, school, etc. If 2G or 3G is also turned on, it isn't transfering data, but, is it consuming battery juice? just a little? or a lot? or none?
It's just that i'm lazy and think it's better that when I leave a wifi area, the phone keeps connected and I wouldn't have to remember to turn it on.
I don't like to use any kind of auto toggler or anything like that, and if it doesn't use battery, think my life would be easier

Thanks!