First we would have to define what you mean by “nicely done.” Are you satisfied with Ikea cabinetry? Do you dream of bath fixtures from Waterworks? Or are you interested in re-purposing high-end cabinetry from a firm like Green Demolitions? Custom cabinetry, while more expensive, can often solve tricky spacial issues like diagonal walls, whereas the Home Depot product, costing less up-front, might still require retrofitting and cost more in the end than the custom product does to begin with! Does $600.00 for a powder room faucet offend you? Does $1000.00? What kind of flooring is being considered? Wood plank, vinyl, stone? Do you want hollow doors or solid? What type of hinges and pulls? What about your counter surfaces, kitchen and bath tile, appliances and lighting? Does your project require an architect? A contractor? Board approval? Department of Buildings filing fees? An interior designer? And all this before you talk about furniture!
There are myriad moving parts to any project and endless decisions to be made that will affect your life for a long time to come. Each item should be considered carefully for looks, for utility and for expense; and with professional input over the entire span of your project.
As a guideline, I would start with $400.00 per square foot; and know that the sky is the limit!