It's your money and sober evaluation of fabrication skill and tools available.
I would not buy anything off ebay, I actually shut down my account there.
Aftermarket headlight assey-s tend to be not sealed properly, get moisture inside and reflective coating varnish in short time. If you have good functional OEM headlight, it will always be superior to AM one.
Plus, you will have to pay for return, right?
Then again, it will cost you quite a bit to fix it anyway, if you already do not have all the tools and materials. I do. So for me, it's about 30 min cakewalk.
Thus, it's your call. If you were to keep that Prius till wheels fall off - I'd fix it, if not - buy AM one and replace.