Car Parts Value..???

Not sure if this is the right forum for this question, but I have a dilemma and I'm hoping someone here has an answer or can point me in the right direction.
I recently purchased a 72 Demon grille from a private seller. Condition was "near mint". No broken/cracked/damaged "fins".. ALL mounting tabs, not only there and intact, but in phenomenal condition, however, there is a previous repair done to one tab....not disclosed by the seller(AssClown). Seems that most tabs are brittle and ready to fall apart on most grilles I've seen...This grille appears to have been off the vehicle and/or out of the elements for a long time. The Bezels are in "near mint" Condon as well.
I paid $400 for this grille, which I thought was a really good price, but I did also pay for shipping($114) and "professional" packaging($60) from an authorized FedEx shipper, Mailboxes Plus. Total for grille and bezels, $574. Shipping cost included extra insurance, which I put a declared value of $1000 on it.
When grille arrived at my office, I set up my camera to record opening the package (something I've always done because of past issues). I recorded condition of box, which there was some obvious "crushed in" areas at the ends of the box. As soon as I get the grille out, I immediately noticed one end of the grille was loose.. After removing several layers of the large bubble wrap and cardboard bracing, I found the break...about the last 5 inches of grille was broken in two. The other end of grille was cracked in about the same area.
I filed a claim with FedEx, which is a pain, and sent in a boatload of pictures, including the invoice from PayPal(friends and family, unfortunately). I informed FedEx that I had a complete video of unpacking and was told to upload it to the claim page, but there's a 4mb limit so I wasn't able to.
My claim has been denied several times because they keep asking for specific pictures etc.. Now that I think they have all pictures needed, they're asking me to prove the value. So, after that long, boring story, HOW DO I PROVE THE VALUE...?
At first they were telling me that it's based on what I paid, but I explained that if I buy an item worth $10,000, but get a deal and only pay $1000, the value of the item is still $10k... That's why I put a declared value of $1000 on this grille. Based on what I've seen with prices and conditions, I wanted to cover my cost of grille, shipping, etc...
I mean, if they want to find me another grille in near mint condition and call it good, be my guest and good luck..! I looked for almost 2 years for a grille that didn't have to have some repair or some issue.. This was the best one I've seen..and again, to me, at a good price.. So, how do I "prove" value on a hard to find, classic car part..???

Thanks,
John