CMASS,
Some great insight here already.
It sounds like your son has some solid opportunities. Congratulations! A very nice D2 conference in your neck of the woods and a ton of wonderful D3s.
It's worth asking for more at the D2 or D3 schools in my experience. As JCG noted, some schools are need based financial aid only and if you don't have the need you don't get the $. Asking doesn't help. And at other schools that offered merit money, we found a wide variation in what schools were willing to do, probably as Fenway notes.
My older guy transferred last year and was awarded very little at his favorite school, and nearly a full ride at some of the D2s. He asked for more from his favorite school and got more, though nowhere near the "almost free" scenarios we had from a few other places.
My 2016 had awards ranging from zero $ to over half of all costs. Merit money played a huge factor for him (and us). A few schools asked if the awards were sufficient. When 2016 said he was not going to attend, they (admissions and the coaches) asked if more merit money would change his mind. That wouldn't happen at Amherst or Williams (at least for him), but it definitely happens at schools further down the rankings and that have merit money to give.