I just did our RED package on a budget, too. This stuff is pretty bomb-proof, so I wouldn't worry about buying used if you can.
Check out all of the aftermarket monitors, and take a look at Ultralight Control Systems for arms. A much cheaper alternative, and very versatile. I would also get both top handles for carrying it around, and don't try to plop it on a tripod that isn't rated for the weight. All of your savings will be for naught if your rig takes a nose dive and you drive glass shards into your sensor.
Skip the case for now, unless you plan on traveling. If it's staying in the school, just keep it deep on a shelf.
ps. Oh, and I agree with the CF card reasoning. These files get big, quick. If your students are forced to keep the shots short and sweet, post work will be much less frustrating as they won't be stalling their computers with huge files. Plus the CF cards, while easier to loose, are cheaper to replace and maintenance free.