@cinnamon1212 thanks, but no easy answer IMO.
Quick thoughts -
Based upon your son’s academic accomplishments, it seems that there was at least as much focus on academics as baseball. But, if baseball is the priority now, I would probably just make a list of D3 schools with an acceptable major and email each and every coach. Maybe obvious but if you go a level down academically, you have some chance of hitting your financial need. You will find that larger D3’s with fin/accounting are few. To make matters worse, D3 recruiting is 3/4 complete right now. You may even lead with the academics with the coaches to get them more interested.