I've just recently fixed my netbook (today)
i cracked my lcd (like yours)
This will help you, http://www.laptopscreen.com/English/model/IBM-Lenovo/IDEAPAD
it has some videos on how to replace the lcd screen (easy), but for the plastic, have you tried to remove the lcd screen, by removing the screws and tried bending it back? or putting a heavy weight on it overnight.
look around for new lcd screens, your be able to get them cheaper.
Hoped i helped, good luck!