What they're fitting to is often an issue too. There can be a lot of movement in suspended timber floors and bathrooms don't always use moisture resistant plasterboard. Many of the big shower enclosure and tray manufacturers also state that tanking is required and without it, any warranty is void.
Not sure what tanking is but having got a full revamp lately, In the quote I had Labour and material to re-slab walls which came to €600. I also had Stripping tiles/Preparation of floor which came in at the same roughly.