It costs about $2,000 total, I think, including all the visits to tighten them and everything.
You do have to wear braces when you sleep. Braces are basically pieces of metal cemented to your teeth. The pieces of metal have holes that they can run a wire through, and the wire is in the shape that they want your teeth to be in. Braces won't just fall off your teeth, either. If one does come un-attached, it will just stay on the wire until your orthodontist can reattach it. (They won't come off in your sleep to choke you, don't worry!)
You probably know this, but grinding your teeth is really bad for them. Try not to do that!
You CAN eat steak, just be careful not to rip it too much or it will hurt.