Well could you just take a piece of plastic or sheet metal and screw it on to the existing fender and bondoe and paint it?
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Doing the same thing the right way would not be a great deal more costly because either way you need bondo and paint. Modifying fenders isn't that bad for a body shop or a good guy with a welder. Anything with a seam of two unlike materials will crack.
All Grand Prix, all the time. 69 Model J, 99 GT & GTP coupes. All junk, haha.