Here are some links to suppliers to give you an idea of the cost. There are others. Just search online using just the part number in the search box to get results.
Hi,
I think that this is the part they you are seeking.
Here is the Lenovo part number: 5CB0F78835
It is from the service manual for your laptop .
Here is a link to the manual. The part is listed on p.96 as RJ45 Door C Y50-70 etc.
https://download.lenovo.com/consumer/mobiles_pub/lenovo_y40_50_series_hmm.pdf
Here are some links to suppliers to give you an idea of the cost. There are others. Just search online using just the part number in the search box to get results.
https://lenovo.encompass.com/item/10203048/Lenovo/5CB0F78835/Co_covers
http://www.impactcomputers.com/5cb0f78835.html
Hopefully this is of some help.