Got caught on a parking space bump stop today. Do I need to replace my entire bumper or can I just replace the lowest part of it?

 

I am fairly sure the x200 is a one piece shell as the later x202 etc.
Bumpers are usually and often repairable and from the look of your photo that damage is likely very repairable. Sometimes however it may be cheaper just to buy a second hand unit. And if you are really lucky in the same colour but most second hand units are not going to be perfect.
A repair will need to be reinforce braced, glued, sanded, resprayed etc etc but comes up like new.

 

It is a one piece shell. Take to body shop. They can repair that.