Verizon iPhone 4 replacement screen help

hi all,

my friend's iphone 4 screen cracked and i was wondering what do i need to replace the screen. im not sure if anything is faulty, but i can see some light when i charge it.

i did some research and the only thing i was able to find was

1) replacement tool kit with screwdriver, five star type screwdriver, pick, suction cup
2) glass screen
3) digitizer

i've seen some on ebay for really cheap ($10) but i think that's only for the glass screen? the one's i found that includes the glass screen and digitizer is around $25-$30.

can i just buy the glass screen or do i have to get it with the digitizer as well?

thanks all.