damaged tail light- repair?

I backed into a workman's saw horse and broke out a piece of the red plastic. Can just the outer shell be replaced or repaired?

You didn't mention what year your car is but typically new replacements (left or right) are around $360+ each (if you can get them). To repair yours you would have to separate the front and back half of your housing and then reseal the two halves back together so they don't leak. Chances are you will damage the two halves trying to get them apart or it will leak once reinstalled, or both.

I'd look for used assemblies in the For Sale section or post a WTB ad.