$4k, or around £3k sounds about right to me too. Maybe £3.5k for starters, if really A1.
But any bike that hasn't been run for years needs checking out, and recommissioning. I wouldn't buy it until I could at least hear the engine running!
Fuel ages and changes chemically over time. If it won't burn you'll have fun purging the old fuel from the injectors! Also, bores will be bone dry as will most of the oil pressure fed bearings, if engine hasn't been run for years. So, take a plug out of reach cylinder, put 10ml of oil into each one, then gently turn engine over to lubricate the bores and pump oil round the engine without any load. Reinsert plugs, make sure battery is fully charged, and hope it will start!
Also, the compound that keep tires supple apparently only works when they are being run. If stored for 5 or more years, the compound can become hard, hence you may need a new set of tyres for starters.
That's probably a worst case scenario... but worth checking.