I should have labeled these as boarding schools. Hard to compare day schools to the expenses of a boarding school, but to answer your question:
Harvard-Westlake is $64k per student (Gr 7-12, 2023).
A couple of other Cali day schools:
Nueva: $68k (K-12).
Flintridge Prep: $56k (7-12).
The figures for somewhat smaller schools (Thacher, Groton, St. Paul’s) are skewed upwards due to some fixed costs spread over fewer students, and conversely the figures for larger schools (Exeter, Lawrenceville, Andover, Choate) are skewed downwards due to some fixed costs spread over larger student bodies.