I agree. It's a Siamese/thai police carbine.

As for price, ther market is small despite the rarity as they aren't really core Japanese items and not alot of guys collect siamese weapons. Arisakaicon collectors may or may not be interested.

I'd expect it to be priced less than $400 in virtually every market. In some cases, MUCH less.

It has NOTHING to do with Paratroopers.