While it's easy to replace a light or faucet at a later date, you should have your contractor do the larger tasks at the same time. If you plan to replace the tub and install tile floor, it's best to do that all at once. You may save on labor charges if they can do a few tasks in one day instead of doing these tasks on separate days a few months apart.
To give you more of an idea of what you'll pay before a contractor gives you an estimate, here are several cost examples for remodels of different size bathrooms, provided by Thumbtack Pro Viewpoint NW, a bathroom remodeler in Vancouver, Washington. Keep in mind each job was specific to that house. The total cost of each project includes all material and labor costs:
There are so many beautiful things to notice about this bathroom that it's hard to know where to start. The concrete sink? The wallpaper? The sconce lighting? The tarnished mirror on the door, reflected in the main mirror? The barely-there ultra-modern faucets? Whatever you notice first, though, you can't but admit that this space is a masterpiece.