About £50 a time - google - lgv medical
My GP wanted to charge the BMA approved fee, at the time £120, so I found an alternative source at £80 which rose to £100 in later years.
Demand has created a wider source and lower prices for D4 medicals but they are not always conveniently located. I could have paid £60 but needed to travel 50 miles to do so.
I am surprised that the BMA charges such a high fee for a requirement needed by working people. I was told that the assumption is that the employing company involved pays the fee. Not in my case as an agency driver!