We got quotes of £5-7k for labour plus basic parts for our en-suite. I did (most of) it myself for £4.6k using high quality materials and fittings.
£1k building materials (things you don’t see)
£2.8k parts (things you do)
£250 external labour (some copper plumbing and fitting aqua panels)
Edit: it’s a walk in shower and sink in there only, so no #40k rolltop bath to contend with.