The ones doschicos mentioned are what come to my mind too. Maybe add Reed though it’s a bit more competitive. There are some small west coast universities to consider too: Loyola Marymount, Santa Clara (both Jesuit).The 5-Cs in Claremont are not really mid-tier but Pitzer is test-optional anyway. If Texas is of interest: Trinity University, Southwestern University.
Merit aid: I know Whitman, LMU, L&C and Trinity are pretty generous but not sure what stats are required.
Best of luck getting your son to engage in the process-- my 2 daughters are all over this college search stuff and my son, who is their academic equal, is just not!