Great feedback so far. I'll just expand on the "level of interest" aspect. One red flag is that you state he doesn't have the velo for a D1 P. Generally, a D1 SS must have a very strong arm also. I know you mentioned that maybe he could be steered to another position, which is correct, but how hard will a D1 want to recruit him if the arm strength isn't there going in? You didn't mention the actual throwing velow, so we don't know just how much of a gap there may be.
On the other hand, you say they have expressed interest and have been responsive with communication. That can certainly be a good sign. Are they responding to your son's exchanges or are they initiating? There is another thread going about coaches not responding or calling back when they say they will. Generally, HA's are more likely to be responsive because the have a much more limited pool to work with so they are both more able and they have to. My suggestion would be that it is time for your son to ask specifically where they see him fit in the program, where he is on their board. It's fine to use the event as a trigger. "I am very interested in XYZ U. and we are considering coming to the camp but it is a cross-country financial commitment for us so I wanted to ask..." And, definitely, as others have suggested, ask about making the trip worthwhile with a school tour, etc.
It's also probably time to ask yourselves some more top-level questions about fit and affordability of the school. i.e. - If they don't have much baseball money to provide (many HA D1's don't), what will tuition be based on any academic or other money he may qualify for? etc., etc.
Be aware that most of these camps are open to all and not just players they are recruiting. So, you won't really get that measure of comparison with who he may be up against (in case that is part of what you meant by "giving him a reality check").