They want "proof" though. I obviously don't have a receipt for the item when I had it new, so all I could provide them is the eBay sale.   They won't accept that though. They want COST price.

Isn't the value of an item is determined by how much someone is prepared to pay for it?  

Either way, if AP are going to quibble over a difference of $10 they're even more ridiculous than I thought!