Do I have to replace the LCD if the iPad screen is cracked?
If the LCD screen is not damaged (no dead pixels) then you probably only need to replace the actual glass front touch panel, or digitizer, and do not need to change the LCD.  This can pick up relatively cheaply ($90, or eBay). You just prise the front panel off, and leaving the LCD in place, replace it with a new one.

Google for this video "How to: Fix a broken front panel on your iPad 2 or iPad 3" on youtube. It give you a good idea of what is involved. Or check out Repair Ipad 2 Glass

To be honest, you are probably better sending it to a third party to get the digitizer replaced.

Good luck.