All that stuff is over-priced due to it's heritage. If you really want to buy a 500 V4 GP bike....
http://www.suterracing.ch/en/suter500.html
Buy a brand new one from the guy who developed the Roberts, Ilmor and Kawasaki MotoGP chassis'
From MCN, the world's number one motorcycle publication
www.motorcyclenews.com
MotoGP/500GP chassis and engine-builder Suter Racing is launching the bike it says fills the gap where a ‘real bike’ should be – for well-heeled trackday addicts. Pitching it as the ‘two-stroke Desmosedici’ – a factory GP machine for public – the bike will feature a new injected 500cc V4 producing over 200bhp, in an evolution frame based on the gorgeous Ilmor X3. Counter-rotating crankshafts will kill vibration and gyroscopic resistance to turning, and customers will be able to spec the bike up to include carbon wheels, WSB forks and full titanium exhaust.