I've been thinking about this since reading other's ideas on another thread...
I made a quick and dirty cadd model and uploaded it to some printing sites (I guessed dimensions since I was too lazy to go downstairs and measure): way too much $ if they can even do something that size, so I'd guess it's going to have to be a diy project for printing. Not my thing, yet.
I got some injection molding quotes... I would need to buy many units in order to get the cost down below Toyota's cost. Counted that out. Group buys around here don't get into the 1000s
I'm thinking the appropriate method for this particular piece (and for the valance too) is thermoforming, which is simpler to DIY than the large format 3d printing and/or injection molding. I came across this video of some guys DIYing a bike tail section in ABS:
https://www.youtube.com/watch?v=utm5ymA-9dA
Seems like a good top/bottom sandwich/press mold and the method of heating the guys in the video used above could work great to heat/press/trim a bunch of these things at once.
That said, I bought mine from Toyota so I'm not likely to begin this quest. I may be able to get a good scan of the part(s) and get a CNC mold made, but that's going to depend on whether one of my clients wants to do me a favor.