Over here the fees are pretty much descretionary, the gov't sets the maximum and recomends re-test levels etc, but the garage can charge as little as they wish. The introduction of the cumputerised system here over the past couple of years has caused a few problems as it virtually forces the tester to carry out full re-tests for certain failures. But again it depends on what they tell the system it failed on.....
Don't know what the situation is like over there, but over here if you take a car to a garage that you don't know well, and they do repairs, you can pretty much guarantee it will fail on something like brakes/shocks/tyres not because it should fail, but because they are the easiest things to fix for the garage to make extra money on. The best places to go for a fair test are the council run test stations. They don't do repairs so you get a fair test. They do however always charge the full fee, and stick to the re-test guidelines religiously.