Me? I'd pay it. You, you'd sue. It's all good. Neither of us has to understand the other.
No, you have misunderstood completely. I have not represented what I would do in the least. I am simply explaining what Poland has done. I am not Poland and I am not Polish.
Requesting back antiquities items through diplomatic or treaty agreement does not really cost much in the way of money if the country where the item is located actually complies with the treaty. Poland isn't suing the collector. Poland isn't suing the US (not yet, anyway).
If anyone is suing, it will be the collector to try to get the gun back, but as noted in the article cited in the OP, the collector isn't likely to do that. Even if he does sue, he won't be suing Poland because Poland doesn't have the gun. The VA AG filed a complaint asking for the case to be removed, but this complaint isn't against Poland, but against the US government. So this notion that Poland is spending all this money on a lawsuit is a not issue. They have not filed a lawsuit thus far, but simply made a typical request for an antiquities item to be returned.