I think it is valuable to look at the assessment of your son as being a "low D-1" as someone saying to you that he will not play much at all if he goes to a D-1, will ride the bench, and doesn't project as doing anything more than that. I hope that doesn't sound harsh. Because the person who said it is doing you and your son a big favor, especially given the fact he wants to be an engineer. Engineering sections at many schools conflict with baseball practice and engineering is clearly a very demanding major.
If that is the only assessment you have, and you have compared him to other players who are on your summer team, high school, and league who actually went on to play D-1 baseball, and he hasn't received any interest from any D-1 coaches/programs then you should not waste time looking at the D-1 programs unless you simply want your son going to a tryout to say he did it. I think ClevelandDad's advice is right on.