Staying on post is for your benefit, not the Cadets. There are two hotel choices; the Thayer, which is very nice, but very expensive, and is only barely on base, so still a distance from the cadet area and other attractions, and the IHG Army hotel, which looks rough from the outside, but the rooms aren't bad (think old red roof inn quality). It is far less expensive, and has an outstanding location, and is very very convenient. It's near the cemetery. There is also another IHG Army hotel just outside the gate, very close to the Thayer.
If you have refined tastes, better stick with the Thayer. If you are happy with simple and functional, go with the IHG. They both book fast, so don't hesitate if it is a big weekend like A-day or a football weekend.