The cost of your project will be tied to a number of factors including the room size and the quality of materials including the grade of fixtures, cabinets and finishes. Bathroom vanities often eat up the majority of the materials budget. Whether a change to the floorplan is involved will also determine the ultimate cost of your master bath remodel.
Hiring a plumber and skilled workers for important tasks is a must to make the planned new bathroom well-fit. Other than that, you can actually save money if you do minor tasks as mentioned before. In addition to those assignments, you can paint the newly-redesigned bathroom. You can work together with your wife to decorate it. Or you can even invite your children to select which items to be put in it.

20% labor price ---out of the question----I'm a Building Contractor, If you are totally remodeling a bathroom, where is the cost for demo of existing???? Demo can easily run an extra 10%- factors: 1) Age of existing---many factors here to adjust price, 2) Accessibility ---Getting materials out of and to the bathroom, and protecting present surroundings of owner. 3) Cost to dispose of debris 4) Where is the Contractor's O & P ???

If someone was to come at us with their own additional contract, we would probably decide that we had given them enough of our time and move on. As Nick mentions below, the contractors reputation is the one on the line. They have every reason to do right by you. The crooks of the world generally don't have a reputation to stand on, and as a customer it is your job to research who you are hiring. If you can't find anything about them, they probably aren't who you want to be dealing with. If they ask for money upfront, they probably aren't running a stable outfit. We never take a penny upfront. We collect when the job is fully complete even when we are working on weeks long projects.
I have a miserably small master bath with a particle board subfloor (house built 1969), so I must guy it. I bought toilet made for small bathrooms, and plan to pull the cabinet sink, replace with pedestal, raise storage like lighted bulkhead, demolish tile, and widen doorway from 28" to 32". I might gain 6" from tile removal alone, plus but another 6" on entrance with cabinet sink removal. Since large expense is in demolition, I could do that. But, install showers is tricky given the drain leveling so I'll hire a pro for that. Question: gutting, updating and repairing master bath is necessary, but to what extent should I go i, terms of resizing, which would entail bumping out wall into adjoining small room, which then adds expense of finishing that where window placement restricts encroachment. It's a nice older brick house that I bought before I realized the made of lapses and oversights by the home inspector (who also is a local top police official in a town with highly subjective law enforcement). I need to fix, list, well and leave. Any thoughts (and prayers much appreciated).