50 GMC - sorry to hear that you had to pay so much for that fender. I go to swap meets all around the midwest, not to make money but just to look mostly. I have found rear fenders in good shape for under $100, less money if you want to buy a patch panel and install.
Besides scarcity and assumed greed on the suppliers part, higher costs are creeping in to every part of this hobby. Higher shipping costs, swap meet sponsers charging more for swap spaces, higher insurance, higher gas prices to get there and the list goes on and on.
I talked to several vendors at the Springfield, MO swap meet this summer who were going to sell the remainder of thier inventory on E-bay just because it costs too much to do a swap meet anymore and still make a decent return. Can you really blame them? After all some of us are just here for the hobby and to meet a few new/old friends.