I know for a fact that the seller bought that bass for $3500 or less, so it's a pretty significant markup.
Having played the bass, I would pay $3500 for it in a heartbeat-it's an incredible-sounding and playing instrument. My only complaint with it was that it weighed a ton-it's easily a couple of pounds heavier than my Series I, which is no lightweight at 12 pounds.
I've talked to the current seller and he seems like a trustworthy dealer, but all of his instruments are overpriced by a pretty fair margin considering market value.