Your requirements - extreme close-up work and auto-focus - won't always be compatible.

Extreme close-up work, or macro photography (work in which the image captured is larger than the object itself) also doesn't really depend on the camera as much as the lens (though it does exclude certain types of camera - a rangefinder is not very suitable for macro photography, because you need a more accurate viewfinder at very close distances).

You haven't said whether you want to use film or a digital camera, but either way, pretty much any SLR will be suitable, because all offer a range of lenses, and as long as you can get a macro lens, that will do what you need. The Wikipedia page I link to above includes a table of some macro lenses, that will help you compare them.

There are other options, such as reversing rings that will allow ordinary lenses to be used for macro photography - but it's probably going to be a more satisfactory experience to use a dedicated macro lens.

Even a modest SLR will be fine; if you decide that you want to spend more in the future, you'll still have your lenses and other equipment.

The other question is auto-focus. By all means, auto-focus may be useful for your general work, but for macro work, it will often actually be more useful to have good manual control (auto-focus won't always know which particular petal of a flower you want in focus...).

For good manual focus control, a film camera, or a digital camera with a larger sensor and therefore larger, brighter viewfinder, will be better. (I find it very hard to focus without the aid of a focusing patch in the viewfinder; only you will know how well you can do this.)

There may be other modern cameras other than SLRs that are equally suitable, but I am not familiar with them and will have to leave others to comment.

A lightweight tripod should also be accounted for in your budget, and perhaps a reflector.

I don't think you need to worry that any camera you buy will be suitable for a beginner - you'll find that your camera operating skills quickly become honed with practice, whatever you get or use, and you'll need to develop some manual operating skills for your work anyway. However, just about any modern camera will also be suitable for point-and-shoot photography when you want to do that, and will give you excellent results.

It's definitely worth asking your teacher for an opinion, as another answer suggests - but rather than starting by asking which particular camera or equipment to get, I would ask what kind of camera, lenses and so on will suit your needs.