Grand Canyon Advise?

I will be in vegas for 5 days in April and I think the wife and myself would like to take a tour. Any advise? Should we book now or wait? Not looking to do a all day trip wouldn't mind 7 hours or less. Is the airplane or hellacopter(sp?)tour worth the extra money. About how long are you in the air for? Which tour gives you the best bang for the dollar? I am hoping to spend less than $400 for my wife and my self. Any advise you can give this rookie would be helpful.