Anyone know anything about disc brakes?

Are mechanics getting paid £60 per hour? Or is that what the workshop charges? Because I'd also argue that's not the value of their training and experience if more than half of it is going on shop overheads. Maybe it's the bike shop model that's not working properly.

No, I doubt the mechanic is getting £60 an hour but whether you are paying the mech's wage or for the rent on the premises where the work is being done, the insurance that'll pay you out if anything goes wrong, for the consumables like barbs and olives and mineral oil, for initial outlay for the tools and the wear and tear on them as they are used (minimal on a job like this maybe but more of a factor for things like chasing and facing and every tool has a finite service life) the result is the same, it's a cost for the service rendered.

Our choices to perform the work ourselves circumvent most of these costs.