If it's almost one year old, then it might be covered under warranty. If not, then you'll want to get yourself AppleCare as it'll be much cheaper than shelling out for a new screen
But if it's been more than a year, then that means you don't qualify for Applecare, and that unfortunately means you'll have to shell out cash to get it fixed.
I mean if you woke up one morning and there was a small crack on the screen due to a manufacturing defect. Who knows, maybe heat or a slight battery bulge could have caused a crack if the screen wasn't made properly.
But if the OP did something to crack the screen, then yea, you're right, warranty most likely will not cover it