A standard (6×8′) bathroom can be gutted and replaced with new fixtures, fittings, tiles etc for less than $10,000, including labor, and it will look great. Obviously this will vary tremendously depending on personal choices made in materials, fixtures and labor costs in your area. I have done four bathrooms (new tiled floors, bath, toilet, sinks and wall tiles etc) in one apartment building for $12,000 total – but everything was cheap – including the labor! On the other side of the spectrum, I have installed a very well appointed bathroom for $46,000. In this case all appliances were top-of-the-line and the ceramics were imported marble. In fact the counter tops, wall and floor tile made up more than half of the bill.
As an approximation I would say $5-$10K will get you a ‘nice’ replacement bathroom on a budget. An extra $5 or $10K will allow you to splash out on better fixtures, ceramics, molding and finish.
Keep in mind that you will probably not recoup more than $10K on a bathroom in terms of property value, no matter how flashy the fixtures or shiny the tiles are.
New bathrooms will not be too much more. You will need to pay to run waste pipes, vents and electrical cable for lighting. Additional costs will of course be incurred for jetted tubs (need their own fuse) and active ventilation (need power and exhaust pipes). Generally though these costs will be labor and so add only a few hundred dollars to the bill.
If you have weak floors these will need to be reinforced (and level) before installing tubs and trays.
If you want to expand or change the layout of a bathroom, this should not be a major blow to the budget. Moving a wall is only a day’s job. Keep in mind that the most difficult (and therefore expensive)item to move is the toilet. The 3′ or 4′ pipe needs to be pitched to pass code, and adding a new pipe or moving an existing one is a major project.
Contractors often run into problems doing any job. These can be legitimate (and usually expensive!) unforeseen structural or circumstantial problems that have to be dealt with to finish the work. Never take their (our) word for it, however! Always ask to see what the problem is and if you think they are exagerating the situation or are in any way suspicious of their description, get a second opinion. As a rule of thumb, it is always best to add an extra 10% to an estimate, just in case. This way you should avoid nasty surprises.