As with all home improvement projects the price depends on the design and extent of work required, as well as the size of the room. let's go through the different areas.
You need to first decide if you are prepared to install yourself or leave it to a professional. Unless you are qualified as a plumber, tiler or electrician we would advise to use tradesmen. In the longer run you will save time and money.
Either because of the age of the current room or your requirements to change to lighting and wall sockets, there could be sigificant electrical work. Things you may want to add to the room include installing a hair dryer, having sockets for shavers etc, including an extractor fan in the ceiling, and installing a power shower. This could cost around £300-500.
Tiling is more tricky than it looks, particularly if you want all tiles parallel with the same gaps and planned well in to the corners, including the cutting of smaller tiles in gaps. Floor tiles are an additional challenge given their increased thickness - cutting is difficult if you don't invest in quality cutting equipment, and again planning sizes and shapes to complete your area really needs an expert. Look at around £800-1200 (excluding tile costs) for a 12x6 floor area. In terms of the tiles used you could opt for ceramic to keep costs down but on the other hand an investment in marble can really set this room off.

A good part of the budget needs to be set aside for plumbing. Replacing the toilet with something more modern and efficient, installing a shower instead of your bath, and fitting need piping and taps to the sink are a few of the main areas. Expect £700-£1000 for a typical room.
Suites can be around £1000. But you can pay double this something a bit different.
A cost worth remembering when you are budgeting. There's quite a bit to remove and disposing of. The average cost for removing and disposing is around £500.
Electrical work
Price: £300-£500
Time: 5-7 hours
Tiling
Price: £500-£600 (Walls), £300-£500 (Floor), excluding tile costs
Time: 2 days
Plumbing
Price: £700-£1000
Time: 2 days
Gutting and disposal
Price: £500
Time: 6-7 hours
You can find some useful tips on this Mumsnet blog
Which? has a good set of tips including:
An important note on the above prices - all exclude the item cost. With Priceatrade you can build your requirements either as fit only or with the item. Obviously if you supply your own items you will need to ensure they are similar to the ones we show or the price may need to change.
Priceatrade - love your home TM
Spread the word
Discover Priceatrade.com's social media channels and join in.