Lots of driving instructors charge a 'car hire' fee to use their car on the day of your test. This can be up to £100, and that's on top of any lesson fee before the test! Many just charge a lot because - they can get away with it!
I don't do this. My charge is based on the time taken, and nothing else. To allow time to drive to the test centre and have a short warm-up drive means that the 'lesson' usually starts an hour or so before the test start time. By the time the test is over, and we've taken a 'pass piccy', that's at about the 2 hour mark. Then it's just the drive home, let's call that half an hour.
So, that's 2.5 hours, and based roughly on my normal 2 hour rate, the test day fee is just:
Any extra warm-up time to go over manoeuvres or whatever is charged at the normal rate.