Owenski

Looks to have a scotoiler thats run dry.
If he's kept up to the scotoiler for x years then its run out of oil and he's run out of love for the bike its easy to see why a chain could get like that very quickly over this last winter.

I'd buy it at £400-£500 if its HPI clear and a runner then yeah I'd buy it but thats because I already have every tool required and I would do all the work myself. I'd be looking at buying:
Front Wheel bearings,
Brake Lines (Unless they're braided I cant tell from the pics),
Fork Seals,
Fork Oil,
Fork Springs,
Head Bearings,
Lower Link Bearings,
zx6r shock,
Rear wheel bearings (sprocket carrier too),
If its an OEM exhaust I'd replace that, if its an aftermarket I'd repack it.
Chain and Sprocket Set
Brake pads all around,
Brake fluid,
Coolant,
and a monster box of stainless bolts to replace every single one on the bike.
Then the normal service items of oil plugs and filters etc along with the major interval items such as valve clearance and throttle body balance.

But only because I can do that all myself, if I couldn't do that work myself then you're looking at spending a fortune having a garage do it and that IMO would be a deal breaker.