Goatmanatv said "Labour rates for a plumbing company should never be that high unless its an after hours call "
That is actually pretty reasonable for a rate. I don't know where you figure it should be less. Journeyman wage is $37.00/hr. Most people to keep employees you pay higher so you are a good $40/hr. Plus company pays taxes behind the scenes, there is the vehicle to cover, tools, etc.
As for the costing of the apprentice. You should have been aware of the person coming and costing. When I get electrical work done and they send apprentices I get a discounted rate and they also are put fully to work, no watching. And they let me know if it is alright to send them.