Unfortunately your experience is not unusual. As an instructor I cannot understand why test day prices are so high - mine are just going up to 2 hours, which I do not think is unreasonable. After all you get an hour before the test plus the test time itself, which is usually around an hour all in. How the price seems to creep up by an extra hour is beyond me. I think part of the problem is that you are essentially a captive audience. If you don't pay, you don't go for test. A bit mean if you ask me.
The one issue I have is that my diary is divided up into specific time slots (1.5 hours eac) and tests can cut across those. This means that one test can take up two slots in the diary i.e., 3 hours. However, this is my problem and not the pupil's and I have to accept the cost, not pass it on.