I paid about $ 650 for an Opel GT front valance a couple of years ago.
It then got dented in shipping and I was able to file a claim for the value which was accepted as $ 650 by UPS. So I think $ 650 is a fair price then and now. But oddly enough, I wouldn't sell mine for that low now! Someone really ought to put metal reproductions into production. It seems like every GT has a rusted/dented belly pan. (I'm too much of a purist to settle for fiberglass!)
Jonzo