But, you forgot to add the working space, for each Honda will pay a rent, you didn't add electricity, and many more.
A £60 to £100 per hour cost I think is acceptable, a service do need to pay salaries, rent, electricity, pay for tools and also maintenance of tools, if they use a lift table, that will need to be inspected annually for H&S, torque wrench will need calibrations regularly, also they pay insurance, if they botch the job and you get injured that a lot of liability for them.