So, one of my headlights is out. It took a hit from a rock it looks like. Passenger side. Naturally that side is $40 more expensive than the driver’s side assembly. Why?
UPDATE: I don’t know that I need to replace the entire assembly, I’m just preparing for the worst. Hopefully it just needs a bulb.
Further UPDATE: So, a bulb did indeed get the light shining again. Well worth the $8 and 15 minutes of my time. It’s a good thing I have small hands though. What to do about the gouge and hole in the lens, well, that needs further thought.
Not So Fast 
It’s considered a luxury item…kind of like the rearview mirror they put on the passenger side sometimes and onboard navigation and stuff. They price it according to what the market will bear.
Ah, I didn’t know that only one headlight was necessary.
Now it all makes sense.