I agree with collegemom3717 that you should look carefully at the Sciences Po experience. The Reims campus is a small satellite campus located about 100 miles from the main Paris campus. The TGV (Train à Grande Vitesse) can take you from Reims to Paris in about an hour and costs about $60 to $80 roundtrip. European universities offer fewer on-campus activities than American colleges do, so I imagine that Sciences Po Reims students would want to go to Paris often. If you are on a tight budget you would feel constrained.
UC Berkeley might also be a challenge for a tight budget. The university provides housing for only 22% of its students, so competition for nearby apartments is fierce. The New York Times reports that rent for a two-bedroom apartment can run $4,000 per month. A group of Berkeley residents has sued the university to force it to cap its enrollment. This case illustrates the high cost of living for a student in Berkeley.
I recommend that you look closely at the total cost of attendance for your UC Berkeley/Sciences Po Reims option. While it could be an exciting experience, it could easily cost much more than $120k, making its cost comparable with your private options.
Both Williams College and Wellesley College house almost all of their students on campus and almost all graduate in 4 years. They offer numerous on-campus events and nearby activities, as well as junior year abroad options. A student can fully enjoy herself with modest spending money. The cost of attendance quoted in your financial aid package is likely to be realistic.
I have focused on financial considerations, but I think you are weighing two dramatically different experiences. UC Berkeley/Sciences Po Reims will be big university city living. Williams or Wellesley will be a campus-oriented medium-sized college experience. Any one of them can give you a great education and set you up for grad school and beyond.
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