On the cheaper end of things I restored my headlights using the BG headlight restore kit. Comes with some sand papers, wet sanding magic fluid, cleaner, and an epoxy type over coat. Makes the headlight look brand new, but doesn't always last. Used to do the job on my father's ford focus which has huge headlights and after three years the epoxy coat would start to flake at the edges and I'd simply do the job over again. I recently got a headlight out of a junk yard that had been badly yellowed. It's the drivers side and I'd been having trouble finding a non broken one, so I took what I could get. Didn't get a before pic, but after it looks like this.. Don't mind the carbon fibber wrap.
Because of how the grille is made, it will work there too. Not the most correct fix, but the best value.