Depends on make and model but unless it was a REALLY expensive, fairly new 1~3 years, top of the line unit you will be better off buying a new one. Prices are down, technology is better and the cost of the screen is usually 70-80% of the unit cost anyway.
You can only if you can afford it it is so expensive about $400
Maybe, depending on how cracked "cracked" is. If only the glass is cracked, it can be replaced. If you've lost the vacuum, it likely isn't worth repairing. forum.ecoustics.com