MK, that is so awesome that he found such a place. I assume your son has seen several other schools unofficially. I think it's hard not to these days with camps, travel ball, academic trips, etc. Don't discount these things as far as son having some perspective as to what he might like or not.
You said the only remaining question is cost. I would recommend you take advantage of the school's interest and explore in as much depth as possible what the likely academic and other aid (realizing D3 has no athletic $) they may be able to provide. Let them know that your son is very interested but you need to know as close as possible what the bottom line is likely to be. While there will likely be some uncertainties, I'd hold out on any commitment until you have completely explored what information/help they can provide in that regard. We were usually able to get fairly accurate estimates on academic, needs, athletic and grant money from the schools that were offering.