Just watched the youtube clip from a well know youtuber taking a Startech, sister brand of Brabus, Model 3 Tesla round the track.
There are changes to the bumpers new rear wing, side skirts and upgraded alloys for the look. Stiffened lowered suspension, by 30mm and an optional interior upgrade. The cost is $17,000 so over £12,000 for the British market I would guess. The spoiler itself is $450 unpainted or fitted.
Not sure about the rear spoiler and the front bumper looks a little lambo like, however great to see companies starting to take Tesla seriously and desiging some nice aero and other mods.