Difficult to value as it's so dependent on condition, but the mileage is pretty low and there's a rarity factor to consider (although Stelvio is a bit of a marmite colour, so that works both ways...).
If the bodywork's undented, the paintwork and hood are in good nick, the rear wheel arches & floor pan are free of the demon rust, the engine & gearbox work well with no rattles, noises off or oil leaks, and it has a solid history (fsh, a sheaf of invoices/old MOTs, a recent MOT with no scary advisories, new cam belt, and fewer than, say, 5 owners), I reckon it might be worth between £4-5k.
But I'm a tight b&stard.