USPS and eBay are not related, so it doesn't matter if you already opened a USPS claim. You will most likely get denied the USPS claim because you are not the shipper, have no USPS receipt, and actually have no knowledge or proof if insurance was even paid for.
Don't try to "..work it out with the seller..". It is more hassle than anything. Just open an ebay claim for damaged goods received, and you will get a full refund, including all shipping costs.
As I said, just get another figure, complete with box and stand. Why going thru all the hassle, when there is an easy and simple solution.
eBay claim --> Full refund --> New figure.