If you want to take the occasional macro photograph of a watch and its mechanism, which can double as a general purpose camera, you might be better off with a digital compact camera, particularly if you want to stay within or close to your budget. Some of these can produce a very good result, with relatively little hassle.
If you want something more than that, Id suggest thinking about it in this order;
1. Light - can you find a location where you can diffuse good natural light, so that you can produce an image with enough detail, depth of field, and shadows? Id avoid flashes or artificial light as they tend to produce horrible flat images with poor shadows (or a sterile result with no shadow, such as with a ring flash), and speculae which ruin the image.
2. Stability - can you set up a tripod, or a copy stand, where the light is good, which can allow you to take a photograph for several seconds or longer, so that you can use a small aperture to get sufficient depth of field?
3. Composition what sort of images are you looking for, and can you use light & shadow, or textured material, or other items to make the image something other than a document of record? If you have time, look at some of Edward Steichens commercial work, where images of fabric, or cutlery, or matches, have a strong element of transforming imagination which makes them extraordinarily beautiful.
4. Magnification again, what sort of image do you want? A standard 50mm lense with extension tubes can produce a great result, without going to the expense of a dedicated macro lense. At the other end of the spectrum, the Canon MP-E 65mm lens is a great and highly specialised tool, if you want to produce high quality magnifications of a watchs interior mechanism. I dont think there is a Nikon equivalent. Renting one over a weekend is worth considering the extension on the lens, necessary to get the magnification, is worth seeing, and itll be quickly obvious why light and stability need to be thought of first.
5. Finally, camera. You could pick up a decent s/h full frame Canon (1d, or 5d, which could use the MP-E lens) or similar Nikon for a few hundred pounds, which can help keep the costs down compared to new equipment.
I do a little still life work; it's tricky, and quite rewarding when it comes right. This one was taken with a view camera, with bellows extended about twice the lens focal length, and using diffused natural light from a window;