I hate to put it so bluntly--but here goes:
You need to be more proactive on your own behalf, and read more of the info on the eBay site. You should be in the clear without question and receive a full refund, including the shipping and insurance fee.
I searched on the completed Grado RS2 sales and found the item description here:
Grado RS2 Headphones - eBay (item 160196631901 end time Jan-07-08 09:07:51 PST)
First, it's crystal clear that the seller states that the shipping insurance is included in the $15 fee. He did not limit the amount in any way, whatsoever......and, on top of it, you ended it early with the "Buy It Now" option, so there is no question--you paid the seller's asking price, and his quoted shipping fee included insurance.
Second, it certainly seems obvious that the only payment method accepted by the seller was PayPal, and it's clearly shown that the buyer is protected for up to $2,000 on this particular transaction by the Buyer Protection Policy.
It's not your fault that the seller screwed up and didn't properly insure the package, nor that UPS "lost" it and failed to get it back in a timely fashion.
Time's a wastin'.......
file the claim with PayPal right away. Call their customer service and explain what happened--if my experience on a similar situation is typical, they will credit you almost immediately and then get their money back from the seller.