Car Parts Value..???

nodemon said
So, after that long, boring story, HOW DO I PROVE THE VALUE...?

That's going to be a tall order probably. You would likely need to find other sellers asking a grand or better. Maybe do a search for new old stock grilles. Just my two pennies.

nodemon said
including the invoice from PayPal(friends and family, unfortunately)

If tied to a card, can the card company reverse the transaction. Again, just a thought.