the plastic piece isn't expensive its the parts it was protecting that are expensive...

for just that piece get your year and model and look on Amazon I have seen them there for sale.. if not then try Ebay or a local parts store but you might end up having to go to a dealership or maybe a junkyard.. I wouldn't expect it to be too expensive but it depends on the year...

but whatever was damaged that was under that might cost a lot.. I would take a look for damaged parts

see . like here is one

https://www.amazon.com/Engine-Splash-Shield-compatible-Hatchback/dp/B009DJXVDM

probably not the one you need though