Which carries more weight in selecting a college: graduation rate or avg cost of attending?

Note that if your student is a strong student in high school (e.g. A average in high school, 32-36 ACT or SAT equivalent), s/he is more likely to be able to graduate after 8 semesters of school, compared to if your student is just ok in high school (e.g. B average in high school, 20-24 ACT or SAT equivalent).