How much is the Nikon Nikkor 50mm 1.2 AI lens worth?

I know the AIS lens is worth in the 400$-600$, but how much is the AI worth?

If I recall, there's not a huge difference between AI and AIS, and the difference only affected a few film SLR models many years ago.

You can still buy a new one for around $650, used ones. EBay completed listings show they have recently sold for $350 to $600, so I think your estimate is right on - depending on condition.