Andy
I had 3 lessons plus a quick half hour or so before the test. The instructor that I used (same one being used by strontium) told me that it's a rip off that many instructors charge £100 for the use of the car during the test. He told me they usually say it's because of insurance purposes but this is untrue and they use it just to get more money. The car is insured during the test in the same way it's insured during your lessons and there is no genuine reason why they should charge it. It doesn't cost them any more, after all their car is going to be used for lessons and tests all the time. On the day of my test he charged me £30 in total for the half hour and the use of his car. His lessons are £22 each so overall, for everything, he charged me just £96 which I thought was very fair. He's based in Downpatrick, it's a pity you're not a bit closer as he really is a sound guy.