If you figure $90,000 over four years that is still only $22,500 per year, which nets out to be like a state school including room and board.
Your DS might also earn a 1/2 year added scholarship if he really impresses the cadre during his first semester. Keep in mind that different battalions vary their attitude about his as some units prefer to give out more scholarships to different cadets rather than to add extensions.
My DS was accepted The Citadel (OOS) but received no scholarship. So instead he decided to attend a local State school out west at regular tuition. He "walked on" to Army ROTC and ended up earning a campus based 3.5 year scholarship within three months as a freshman.
That was four years ago and he will be commissioning this May as an Armor officer.
His net cost for attendance: The Army paid all but $10,000 of his tuition. He paid for room and board for all four years at an average of $11K per year.
So his total out of pocket for college was $44,000 R&B plus $10,000 freshman tution = $54,000 or $13,500 per year.
Plus he worked two part-time jobs, received an Army monthly stipend and book allowance. For him, it turned out much better than paying about 55K a year ($220K over four years) at El Cid, plus coast to coast airfare back and forth. (and no part time jobs allowed as a knob).