When it comes to USED parts......
How much is YOUR time worth? How much time COULD you spend on the phone...or the internet...looking for a part that would satisfy you both in price and quality. And if you did find a suitable part, how much of your time would you spend removing it from the donor car, how much fuel and expense to get yourself there to take it off, plus the fuel to get you and your part back home????
Factor all of that in, plus the price of the part in the first place, and I'll bet if you did find a fender for $100, you'd have close to $250(or more....) in it when all is said and done.
Just sayin........it ain't all as simple as it sounds.