I don't know about anyone else but my twins put no money at all up front and have been saving since day 1. Of course, the net pay during 4* year is something just over $125/month, but it does go up each year.
They have to pay for uniforms, football season tickets (required to buy the ticket and to attend the game), books and laundry.
My twins will tell you that a ski lift ticket is also necessary! We pay their transportation expenses to/from USAFA which can really add up. Also Bundy, if your child is going to be on the fencing team, s/he must pay his own membership to USFencing ASsoc for USFA tournaments (such as the recent NAC), and they must pay for USFA tournaments. I don't know how it works for other sports.
So, unlike other schools where one puts up $40,000 for tuition and another $10K for room & board, these items are indeed paid for by USAFA. But, there are indeed other expenses.
Also, for later, I believe that some parents pick up the cost of the ring, which can be substantial. The fencers family hasn't crossed that particular bridge yet.