refitting a bathroom is usually "a few" thousand.
Plumbers should be cheaper than glossy high-street showrooms.
You can buy the bits yourself, let them know before getting a price, and be sure you have it all delivered before work starts.. Bristan taps and wastes are very good; Aqualisa showers are very good, Twyfords WCs are very good. Quality of taps and accessories make all the difference. Nothing is as durable as chrome. Avoid pop-up wastes, they leak. I've recently moved to "clicker" wastes (no plug). Ceramic joystick taps are not as reliable as capstan taps.
White baths and basins are cheap and easy to match (there are a few quality bath brands at higher price)
Tiles are cheaper at Wickes than at Tile shops.
Look out for end-of-line bargains
Chrome accessories, I found Wickes, Toolstation, Screwfix and B&Q all sold the range I liked, though the name on the box was different. Once you have found a range you like, you will often find it discounted on fleabay, also taps and showers.
Plumbworld is a good source. Put "clearance" into the search page and see what they have. Architekt is their own budget brand. Ironmongerydirect have vast ranges and may have accessories.