You are correct in all your descriptions about the rifle.
The KFS PU Sniper is a bit of an odd commercial model to value. It's not a Chinese built model, it was made stateside. They are usually made on 974 arsenal receivers, however I have seen ones (like yours) that are not. Most have the shaved bayo lug, the ones with a bayo are not rare, but definitely less common. And they are almost always a mish mash of parts, however they usually shoot EXTREMELY well.
Having the proper scope and mount is a big plus, as they really have no extra value over a regular SKS without them.
The other thing about the value of these, is that most SKS enthusiasts don't know what they are. They really ONLY have extra value to a commercial model collector looking to fill a spot in his collection.
IF you can find the right person looking for one, they often sell in the $450-$500 range just as yours sits.
Hope this helps.