Do you have a Motion? I don't see the Motion listed as the device you have.
If indeed you do have a Motion, what is broken? Is the lcd broken, or the digitizer? A simple search pulled this up for the lcd.
LG Motion 4G MS770 LCD Screen Replacement , thats 16 bucks. I found this for the digitizer
Touch Screen Digitizer Glass Lens Replacement for LG MetroPCS MS770 Motion 4G | eBay
Thats 24 bucks, so if you do it yourself it will only cost you the parts. I would guess and say you can have it replaced by a service tech for around 35-50 bucks. Depending on what it costs to get it replaced, I would just say buy another brand new phone. Good luck.