I got 8% discount in total on 20dSE with quite a lot of extras.
Broadspeed gives a useful starting point for prices but it doesnt take into account extras which it use to. And these must have huge profit margins.
Comments on extras if it helps:
Panoramic Roof - always gone for this, and my wife has on her minis, light and airy feeling, otherwise feels claustrophic and dark
Auto - didnt on last X3 because not available with diesel then, but always had with 3 series estates before.
Visibility pack - adaptive headlamps are good for country lanes, headlamp assist works surprisingly well.
Servotronic sterring - had before since needed to lighten steering, missed it when in other cars.
Professional Media - rip off but needed SatNav. The Business version seems major rip off, so I would either get Professional or not at all. No speed cameras, map colours no very good, clunky controls.
Reverse Camera & Top view - Top view not that useful, but wasnt that much extra. Annoying Front sensor doesnt come on automatically, I am sure it did in my last X3.
Speed limit display - impressive software, OK for price.
With hindsight would have got Comfort access only because its a nuisance pulling key out to open doors then remembering to put in pocket and not have it fall between seats etc.
Didnt get run flats because ride felt much better without but if I have a puncture bet I will regret. Dont mind not having Spare Wheel, on last X3 couldnt get a wheel off when I had a puncture because alloy or wheel had "welded" to steel of brake housing, garage had to use sledge on it - which I couldnt do with the car up on a BMW jack.
Beige - prefer a light inside, black shows up all marks and stuff, beige surprisingly is OK. But not beige in boot. I dont like BMW interiors where its part one colour and part black.