Top of the range Trek Madone is £13,800. That seems to be about the going rate for a dentist's bike these days.
But I can’t imagine anyone spending that much is going to be happy with stock options, so your dentist is going to want to add fancy wheels, another £3k at least, and a power meter, another £1k? Pedals, bottle cages, Garmin - that’s another £1k…
I wouldn’t be averse to spending that kind of money on a bike if I had it, but I certainly wouldn’t be buying a standard production bike for that much.