Back on topic, that PX Ultegra is £899. Take off £50? for the wheels, £300? for the groupset, £100 (probably a massive overestimation) for tubes, tyres, seatpost, saddle, stem, bars, tape, leaves £400. I reckon if they are paying £100 each for those frames they are getting them at a bad price. So around £300 margin on each bike, at a guess. That's not too bad.