So much depends on the school (culture/location/etc.) and the kid.
Since SAS is 100% boarding with few people going home on weekends (so there are plenty of on-campus activities), and pretty much everything’s included in tuition, plus the fact far enough from a town/mall that trips (and hence opportunities to spend $) are not that frequent…7D1 was able to get through 4 years with very little cash burn. Probably $20/week or even less. Maybe $50/month?
7D2 is at Masters, with a smaller boarding percentage, a higher percentage of local boarders going home on weekends (so there’s less on-campus activity on weekends and more people going on mall trips, etc.), and a town center a very short walk away PLUS NYC a short train ride away…and she definitely went through money faster than her sister, at least during her frosh year. Probably about $100/month, not counting train tix.
Again, some of this is about the kid. I think if 7D1 had gone to Masters, she would have ended up spending less than her sister.